Arm Repeat Domain Research Articles

Molecular cloning and expression analysis of <italic>BoPUB9</italic> in self-incompatibility <italic>Brassica oleracea</italic>

<p id="C3">Self-incompatibility (SI) refers to the characteristic that the pistil of a plant can recognize its own pollen and allogeneic pollen so as to inhibit the germination of its own pollen. PUB (Plant U-Box) proteins play an important role in plant stress resistance and signal transduction. In this study, through the analysis of stigma transcriptome data of <italic>Brassica oleracea</italic> self-pollination at 0-60 minute(s), a PUB protein coding gene <italic>BoPUB9</italic> was screened and up-regulated by self-pollination. The <italic>BoPUB9</italic> cDNA sequence was 1368 bp, gDNA of 1720 bp in length, containing one arm repeat domain and one U-box domain. The relative expression levels showed that <italic>BoPUB9</italic> gene was expressed in different tissues of <italic>Brassica oleracea</italic>, and the relative expression level was the highest in sepals, followed by petals, stamens and stigmas, and relatively lower in pollen buds, which was consistent with the results of GUS staining. The relative expression level of <italic>BoPUB9</italic> gene was up-regulated rapidly in self-pollination 0-30 minute(s), the expression level after 15 min was more than 20 times that after cross-pollination, and the difference was the biggest after 30 min, the expression level after self-pollination was more than 40 times that after cross-pollination. Subcellular localization revealed that BoPUB9 protein was expressed in both nucleus and cytoplasm, and BoPUB9 protein was successfully induced in <italic>E. coli</italic>, and the relative molecular weight of 51 kD was consistent with the predicted results. The results of yeast two-hybrid and poll-down indicated that the intracellular domain of SRK interacted with PUB9 protein. It was speculated that <italic>BoPUB9</italic> might be a novel gene involved in the process of self-incompatibility in <italic>Brassica oleracea</italic>, which providing a new content for further research and utilization of self-incompatibility in <italic>Brassica oleracea</italic>.

Identification and characterization of BoPUB3: a novel interaction protein with S-locus receptor kinase in Brassica oleracea L.

Armadillo repeat containing 1 (ARC1) is phosphorylated by S-locus receptor kinase (SRK) and functions as a positive regulator in self-incompatibility response of Brassica. However, ARC1 only causes partial breakdown of the self-incompatibility response, and other SRK downstream factors may also participate in the self-incompatibility signaling pathway. In the present study, to search for SRK downstream targets, a plant U-box protein 3 (BoPUB3) was identified from the stigma of Brassica oleracea L. BoPUB3 was highly expressed in the stigma, and its expression was increased with the stigma development and reached to the highest level in the mature-stage stigma. BoPUB3, a 76.8-kDa protein with 697 amino acids, is a member of the PUB-ARM family and contains three domain characteristics of BoARC1, including a U-box N-terminal domain, a U-box motif, and a C-terminal arm repeat domain. The phylogenic tree showed that BoPUB3 was close to BoARC1. The synteny analysis revealed that B. oleracea chromosomal region containing BoPUB3 had high synteny with the Arabidopsis thaliana chromosomal region containing AtPUB3 (At3G54790). In addition, the subcellular localization analysis showed that BoPUB3 primarily localized in the plasma membrane and also in the cytoplasm. The combination of the yeast two-hybrid and in vitro binding assay showed that both BoPUB3 and BoARC1 could interact with SRK kinase domain, and SRK showed much higher level of β-galactosidase activity in its interaction with BoPUB3 than with BoARC1. These results implied that BoPUB3 is a novel interactor with SRK, which lays a basis for further research on whether PUB3 participates in the self-incompatibility signaling pathway.

Domain architecture of BAF250a reveals the ARID and ARM-repeat domains with implication in function and assembly of the BAF remodeling complex.

BAF250a and BAF250b are subunits of the SWI/SNF chromatin-remodeling complex that recruit the complex to chromatin allowing transcriptional activation of several genes. Despite being the central subunits of the SWI/SNF complex, the structural and functional annotation of BAF250a/b remains poorly understood. BAF250a (nearly 2200 residues protein) harbors an N-terminal DNA binding ARID (~110 residues) and a C-terminal folded region (~250 residues) of unknown structure and function, recently annotated as BAF250_C. Using hydrophobic core analysis, fold prediction and comparative modeling, here we have defined a domain boundary and associate a β-catenin like ARM-repeat fold to the C-terminus of BAF250a that encompass BAF250_C. The N-terminal DNA-binding ARID is found in diverse domain combinations in proteins imparting unique functions. We used a comparative sequence analysis based approach to study the ARIDs from diverse domain contexts and identified conserved residue positions that are important to preserve its core structure. Supporting this, mutation of one such conserved residue valine, at position 1067, to glycine, resulted in destabilization, loss of structural integrity and DNA binding affinity of ARID. Additionally, we identified a set of conserved and surface-exposed residues unique to the ARID when it co-occurs with the ARM repeat containing BAF250_C in BAF250a. Several of these residues are found mutated in somatic cancers. We predict that these residues in BAF250a may play important roles in mediating protein-DNA and protein-protein interactions in the BAF complex.

The E3 ligase OsPUB15 interacts with the receptor-like kinase PID2 and regulates plant cell death and innate immunity.

BackgroundRice blast disease is one of the most destructive diseases of rice worldwide. We previously cloned the rice blast resistance gene Pid2, which encodes a transmembrane receptor-like kinase containing an extracellular B-lectin domain and an intracellular serine/threonine kinase domain. However, little is known about Pid2-mediated signaling.ResultsHere we report the functional characterization of the U-box/ARM repeat protein OsPUB15 as one of the PID2-binding proteins. We found that OsPUB15 physically interacted with the kinase domain of PID2 (PID2K) in vitro and in vivo and the ARM repeat domain of OsPUB15 was essential for the interaction. In vitro biochemical assays indicated that PID2K possessed kinase activity and was able to phosphorylate OsPUB15. We also found that the phosphorylated form of OsPUB15 possessed E3 ligase activity. Expression pattern analyses revealed that OsPUB15 was constitutively expressed and its encoded protein OsPUB15 was localized in cytosol. Transgenic rice plants over-expressing OsPUB15 at early stage displayed cell death lesions spontaneously in association with a constitutive activation of plant basal defense responses, including excessive accumulation of hydrogen peroxide, up-regulated expression of pathogenesis-related genes and enhanced resistance to blast strains. We also observed that, along with plant growth, the cell death lesions kept spreading over the whole seedlings quickly resulting in a seedling lethal phenotype.ConclusionsThese results reveal that the E3 ligase OsPUB15 interacts directly with the receptor-like kinase PID2 and regulates plant cell death and blast disease resistance.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0442-4) contains supplementary material, which is available to authorized users.

The RNA helicase Aquarius exhibits structural adaptations mediating its recruitment to spliceosomes.

Aquarius is a multifunctional putative RNA helicase that binds precursor-mRNA introns at a defined position. Here we report the crystal structure of human Aquarius, revealing a central RNA helicase core and several unique accessory domains, including an ARM-repeat domain. We show that Aquarius is integrated into spliceosomes as part of a pentameric intron-binding complex (IBC) that, together with the ARM domain, cross-links to U2 snRNP proteins within activated spliceosomes; this suggests that the latter aid in positioning Aquarius on the intron. Aquarius's ARM domain is essential for IBC formation, thus indicating that it has a key protein-protein-scaffolding role. Finally, we provide evidence that Aquarius is required for efficient precursor-mRNA splicing in vitro. Our findings highlight the remarkable structural adaptations of a helicase to achieve position-specific recruitment to a ribonucleoprotein complex and reveal a new building block of the human spliceosome.

Suppression of Arabidopsis AtPUB30 resulted in increased tolerance to salt stress during germination.

The Arabidopsis U-box E3 Ub ligase AtPUB30 participates in the salt stress tolerance as a negative factor in an ABA-independent manner during germination. Based on the in silico expression data, the U-box protein 30 (AtPUB30) from Arabidopsis thaliana was identified as a gene that responds to salt stress. The deduced AtPUB30 protein consists of 448 amino acids with a single U-box motif and five ARM-repeat domains. An in vitro self-ubiquitination assay demonstrated that bacterially expressed AtPUB30 exhibited E3 ubiquitin (Ub) ligase activity and that the U-box domain was essential for the activity. Real-time qRT-PCR and promoter-GUS analyses showed that AtPUB30 was induced by high salinity, but not by drought, cold, or abscisic acid (ABA), in roots but not in shoots. These results suggest that AtPUB30 is an Arabidopsis U-box E3 Ub ligase, the expression of which is selectively enhanced by salt stress in roots. T-DNA-inserted loss-of-function atpub30 mutant plants (atpub30-1 and atpub30-2) were more tolerant to salt stress in the germination stage, as identified by radicle emergence, cotyledon opening, and more vigorous early root growth relative to wild-type plants. Thus, it is likely that AtPUB30 plays a negative role in high salinity tolerance in the germination process. Wild type and mutant plants displayed very similar germination rates when treated with ABA, suggesting that the action of AtPUB30 in the germination stage is ABA independent. The post-germination growth of NaCl-stressed wild type and mutant plants were indistinguishable. Overall, our data suggest that the Arabidopsis U-box E3 Ub ligase AtPUB30 participates in the salt stress tolerance as a negative factor in the germination stage in root tissues.

Abstract 1557: Overexpressions of ALEX1 gene play a negative role in human colorectal tumorigenesis

Abstract Background: Arm protein lost in epithelial cancers, on chromosome X (ALEX) is a novel subgroup within the armadillo family which has several ARM repeat domain. The role and the expression profile of ALEX1 gene in colorectal tumor are not well examined. Our studies have revealed overexpression of ALEX1 suppressed colony formation ability of stable human colorectal carcinoma cell lines and clinical significance of ALEX1 expression in colorectal cancer patients. Materials and methods: Human colon cancer cell lines (HCT116, SW480) and breast cancer cell line (MCF-7) were used in this study. Human ALEX1 gene was amplified by PCR and inserted into the XhoI site of pCAGIPuro plasmid. Colony formation assay and Soft agar colony formation assay were performed to examine the effect of overexpression of the ALEX1 on cancer cell proliferation. Genomic DNA was purified by the phenol chloroform extraction and bisulfite genomic sequencing was carried out with the EpiTect bisulfite kit. We examined the expression level of ALEX1 mRNA in matched tissue pairs of normal colorectal mucosa and colorectal tumor tissue by Quantitative real-time RT-PCR Tumor specimens along with adjacent normal tissues were obtained from 49 patients with primary colorectal cancer undergoing complete surgical resection of tumors and lymph nodes. The pathological stages of the patients were as follows: stage I, 9 patients; stage II, 16 patients and stage III, 24 patients by pTNM classification. The post-surgical observation period was from 277 to 3631 days (1625.0 ± 1033.0 days). Results: Overexpression of ALEX1 in colorectal carcinoma cells was capable of impairing colony formation and suppressed the anchorage-dependent and -independent colony formation of human colorectal carcinoma cell lines by the study of stable clones of HCT116 cells expressing ALEX1 protein. Bisulfite genomic sequencing revealed that the promoter region of ALEX1 gene was highly methylated in both HCT116 and I SW480 cells in comparison to those in PANC-1 and MCF-7 cells which express endogenous ALEX1 mRNA, indicating the capability of promoter methylation to silence ALEX1 gene in HCT116 and SW480 cells. In 34 cases out of 49 (69%) colorectal tumor tissues, greater than a 50% reduction of the ALEX1 mRNA level was observed in comparison to adjacent normal mucosa tissues. ALEX1 mRNA was significantly reduced in colorectal tumor tissues than those in normal mucosa (P=0.01459, Mann-Whitney U-test). The 17 cases with higher ALEX1 gene expression (Tumor/normal value ≧0.20) significantly revealed a better disease-free survival rate than the other 32 cases (&amp;lt; 0.20; P = 0.045, log-rank test), which showed significant correlations between ALEX1 expression and better prognosis. Conclusions: Our findings may support that ALEX1 functions as a tumor suppressor in colorectal cancer progression. Examination of ALEX1 expression might be helpful for predicting the prognosis of patients with curative resected colorectal cancer. Citation Format: Akihiko Takeda. Overexpressions of ALEX1 gene play a negative role in human colorectal tumorigenesis. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 1557. doi:10.1158/1538-7445.AM2014-1557

Kinesin-II recruits Armadillo and Dishevelled for Wingless signaling in Drosophila

Wingless (Wg)/Wnt signaling is fundamental in metazoan development. Armadillo (Arm)/β-catenin and Dishevelled (Dsh) are key components of Wnt signal transduction. Recent studies suggest that intracellular trafficking of Wnt signaling components is important, but underlying mechanisms are not well known. Here, we show that Klp64D, the Drosophila homolog of Kif3A kinesin II subunit, is required for Wg signaling by regulating Arm during wing development. Mutations in klp64D or RNAi cause wing notching and loss of Wg target gene expression. The wing notching phenotype by Klp64D knockdown is suppressed by activated Arm but not by Dsh, suggesting that Klp64D is required for Arm function. Furthermore, klp64D and arm mutants show synergistic genetic interaction. Consistent with this genetic interaction, Klp64D directly binds to the Arm repeat domain of Arm and can recruit Dsh in the presence of Arm. Overexpression of Klp64D mutated in the motor domain causes dominant wing notching, indicating the importance of the motor activity. Klp64D shows subcellular localization to intracellular vesicles overlapping with Arm and Dsh. In klp64D mutants, Arm is abnormally accumulated in vesicular structures including Golgi, suggesting that intracellular trafficking of Arm is affected. Human KIF3A can also bind β-catenin and rescue klp64D RNAi phenotypes. Taken together, we propose that Klp64D is essential for Wg signaling by trafficking of Arm via the formation of a conserved complex with Arm.

Structural insight into the function of the spliceosomal helicase Aquarius

Beyond participating in splicing, some spliceosomal components from higher eukaryotes play pivotal roles in coupling splicing to other RNA-processing events. The massive spliceosomal helicase Aquarius (170 kDa) is loaded at a specific location on the intron, where it acts as a molecular linker between splicing, the deposition of the exon-junction complex on the mRNA and the formation of snoRNPs from intronic segments. We have determined the crystal structures of the full-length Aquarius in complex with a non-hydrolysable ATP analog as well as with a single-stranded RNA. The structure reveals a complex molecular architecture, with a central core that resembles the RNA helicase Upf1 surrounded by several specific domains. Among them we identify an ARM-repeat domain, plus three other domains that were not observed in helicases. We could evidence that Aquarius possesses motor activity in vitro and that, strikingly, it exhibits opposite unwinding polarity versus Upf1. Crystal structure of Aquarius in complex with RNA revealed a novel mode of RNA binding by a helicase and led to the identification of structural adaptations underlying the reversal of directionality. Overall, the structure-function analysis brings insightful implications into the manner how two helicases have diverged from a common ancestor as a mean to achieve opposite polarities of translocation. Furthermore, we demonstrate that Aquarius is recruited to the spliceosome in complex with four other splicing factors and that the ARM domain is essential for the integrity of the complex. Moreover,the ARM domain makes contacts in the spliceosomal core, providing insight into the molecular basis underlying the accurate positioning of Aquarius on the intron. Following the line of these findings, we finally show that Aquarius plays an important role for the occurrence of splicing per se.

Kinesin-II recruits Armadillo and Dishevelled for Wingless signaling in Drosophila.

Wingless (Wg)/Wnt signaling is fundamental in metazoan development. Armadillo (Arm)/β-catenin and Dishevelled (Dsh) are key components of Wnt signal transduction. Recent studies suggest that intracellular trafficking of Wnt signaling components is important, but underlying mechanisms are not well known. Here, we show that Klp64D, the Drosophila homolog of Kif3A kinesin II subunit, is required for Wg signaling by regulating Arm during wing development. Mutations in klp64D or RNAi cause wing notching and loss of Wg target gene expression. The wing notching phenotype by Klp64D knockdown is suppressed by activated Arm but not by Dsh, suggesting that Klp64D is required for Arm function. Furthermore, klp64D and arm mutants show synergistic genetic interaction. Consistent with this genetic interaction, Klp64D directly binds to the Arm repeat domain of Arm and can recruit Dsh in the presence of Arm. Overexpression of Klp64D mutated in the motor domain causes dominant wing notching, indicating the importance of the motor activity. Klp64D shows subcellular localization to intracellular vesicles overlapping with Arm and Dsh. In klp64D mutants, Arm is abnormally accumulated in vesicular structures including Golgi, suggesting that intracellular trafficking of Arm is affected. Human KIF3A can also bind β-catenin and rescue klp64D RNAi phenotypes. Taken together, we propose that Klp64D is essential for Wg signaling by trafficking of Arm via the formation of a conserved complex with Arm.

Structural insights into the novel ARM-repeat protein CTNNBL1 and its association with the hPrp19–CDC5L complex

The hPrp19-CDC5L complex plays a crucial role during human pre-mRNA splicing by catalytic activation of the spliceosome. In order to elucidate the molecular architecture of the hPrp19-CDC5L complex, the crystal structure of CTNNBL1, one of the major components of this complex, was determined. Unlike canonical ARM-repeat proteins such as β-catenin and importin-α, CTNNBL1 was found to contain a twisted and extended ARM-repeat structure at the C-terminal domain and, more importantly, the protein formed a stable dimer. A highly negatively charged patch formed in the N-terminal ARM-repeat domain of CTNNBL1 provides a binding site for CDC5L, a binding partner of the protein in the hPrp19-CDC5L complex, and these two proteins form a complex with a stoichiometry of 2:2. These findings not only present the crystal structure of a novel ARM-repeat protein, CTNNBL1, but also provide insights into the detailed molecular architecture of the hPrp19-CDC5L complex.

Plasma membrane-association of SAUL1-type plant U-box armadillo repeat proteins is conserved in land plants

Post-translational protein modification plays a pivotal role in the regulation and specific turnover of proteins. One of these important modifications is the ubiquitination of target proteins, which can occur at distinct cellular compartments. At the plasma membrane, ubiquitination regulates the internalization and thus trafficking of membrane proteins such as receptors and channels. The Arabidopsis plant U-box (PUB) armadillo repeat (PUB-ARM) ubiquitin ligase SAUL1 (SENESCENCE-ASSOCIATED UBIQUITIN LIGASE1) is part of the ubiquitination machinery at the plasma membrane. In contrast to most other PUB-ARM proteins, SAUL1 carries additional C-terminal ARM repeats responsible for plasma membrane-association. Here, we demonstrated that the C-terminal ARM repeat domain is also essential and sufficient to mediate plasma membrane-association of the closest Arabidopis paralog AtPUB43. We investigated targeting of PUB-ARM ubiquitin ligases of different plant species to find out whether plasma membrane-association of SAUL1-type PUB-ARM proteins is conserved. Phylogenetic analysis identified orthologs of SAUL1 in these plant species. Intracellular localization of transiently expressed GFP fusion proteins revealed that indeed plasma membrane-association due to additional C-terminal ARM repeats represents a conserved feature of SAUL1-type proteins. Analyses of transgenic Arabidopsis plants overexpressing N-terminally masked or truncated proteins revealed that interfering with the function of SAUL1-type proteins resulted in severe growth defects. Our results suggest an ancient origin of ubiquitination at the plasma membrane in the evolution of land plants.

Role of overexpressions of ALEX1 gene in human colorectal tumorigenesis.

443 Background: Arm protein lost in epithelial cancers, on chromosome X (ALEX) is a novel subgroup within the armadillo family which has several ARM repeat domain. Our studies have revealed that overexpression of ALEX1 suppressed colony formation ability of stable human colorectal carcinoma cell lines. But clinical significance of ALEX1 expression in colorectal cancer patients is largely unknown. Methods: We examined the expression level of ALEX1 mRNA in matched tissue pairs of normal colorectal mucosa and colorectal tumor tissue by quantitative real-time RT-PCR Tumor specimens along with adjacent normal tissues were obtained from 49 patients with primary colorectal cancer undergoing complete surgical resection of tumors and lymph nodes, followed by adjuvant systemic therapy in some cases. All tissue samples were stored at -80°C until use. The 49 colorectal specimens comprised 26 well-differentiated and 23 moderately-differentiated adenocarcinoma. Corresponding extraneoplastic normal colon tissues from the same 49 patients were also examined. The pathological stages of the patients were as follows: stage I, 9 patients; stage II, 16 patients and stage III, 24 patients by pTNM classification. The post-surgical treatment observation period was from 277 to 3,631 days (1625.0 ± 1033.0 days). Results: In 34 cases out of 49 (69%) colorectal tumor tissues, greater than a 50% reduction of the ALEX1 mRNA level was observed in comparison to adjacent normal mucosa tissues. ALEX1 mRNA was significantly reduced in colorectal tumor tissues than those in normal mucosa (p=0.01459, Mann–Whitney U-test). The 17 cases with higher ALEX1 gene expression (tumor/normal value ³a0.20) significantly revealed a better disease-free survival rate than the other 32 cases (&lt; 0.20; p = 0.045, log-rank test), which showed significant correlations between ALEX1 expression and better prognosis. There was no significant relationship between ALEX1 expression and the other clinicopathological features. Conclusions: Our findings may support that ALEX1 functions as a tumor suppressor in colorectal cancer progression. Examination of ALEX1 expression might be helpful for predicting the prognosis of patients with curative resected colorectal cancer.

Arabidopsis Fused kinase and the Kinesin‐12 subfamily constitute a signalling module required for phragmoplast expansion

The conserved Fused kinase plays vital but divergent roles in many organisms from Hedgehog signalling in Drosophila to polarization and chemotaxis in Dictyostelium. Previously we have shown that Arabidopsis Fused kinase termed TWO-IN-ONE (TIO) is essential for cytokinesis in both sporophytic and gametophytic cell types. Here using in vivo imaging of GFP-tagged microtubules in dividing microspores we show that TIO is required for expansion of the phragmoplast. We identify the phragmoplast-associated kinesins, PAKRP1/Kinesin-12A and PAKRP1L/Kinesin-12B, as TIO-interacting proteins and determine TIO-Kinesin-12 interaction domains and their requirement in male gametophytic cytokinesis. Our results support the role of TIO as a functional protein kinase that interacts with Kinesin-12 subfamily members mainly through the C-terminal ARM repeat domain, but with a contribution from the N-terminal kinase domain. The interaction of TIO with Kinesin proteins and the functional requirement of their interaction domains support the operation of a Fused kinase signalling module in phragmoplast expansion that depends upon conserved structural features in diverse Fused kinases.

α-Catenin contributes to the strength of E-cadherin–p120 interactions

Cadherin-catenin interactions play an important role in cadherin-mediated adhesion. Here we present strong evidence that in the cadherin-catenin complex α-catenin contributes to the binding strength of another catenin, p120, to the same complex. Specifically, we found that a β-catenin-uncoupled cadherin mutant interacts much more weakly with p120 than its full-size counterpart and that it is rapidly endocytosed from the surface of A-431 cells. We also showed that p120 overexpression stabilizes this mutant on the cell surface. Examination of the α-catenin-deficient MDA-MB-468 cells and their derivates in which α-catenin was reintroduced showed that α-catenin reinforces E-cadherin-p120 association. Finally, a cross-linking analysis of the cadherin-catenin complex indicated that a large loop located in the middle of the p120 arm-repeat domain is in close spatial vicinity to the amino-terminal VH1 domain of α-catenin. The six amino acid-long extension of this loop, caused by an alternative splicing, weakens p120 binding to cadherin. The data suggest that α-catenin-p120 contact within the cadherin-catenin complex can regulate cadherin trafficking.

Parallel Duplication and Partial Subfunctionalization of -Catenin/Armadillo during Insect Evolution

β-Catenin is a multifunctional scaffolding protein with roles in Wnt signaling, cell adhesion, and centrosome separation. Here, we report on independent duplications of the insect β-Catenin ortholog armadillo (arm) in the red flour beetle Tribolium castaneum and the pea aphid Acyrthosiphon pisum. Detailed sequence analysis shows that in both species, one paralog lost critical residues of the α-Catenin binding domain, which is essential for cell adhesion, and accumulated a dramatically higher number of amino acid substitutions in the central Arm repeat domain. Residues associated with aspects of Wnt signaling, however, are conserved in both paralogs. Consistent with these molecular signatures, the effects of specific and combinatorial knockdown experiments in the Tribolium embryo indicate that the duplication resulted in redundant involvement in Wnt signaling of both β-Catenin paralogs but differential inheritance of the ancestral cell adhesion and centrosome separation functions. We conclude that the duplicated pea aphid and flour beetle β-catenin genes experienced partial subfunctionalization, which appears to be evolutionarily favored. Providing first evidence of genetic separability of the cell adhesion and centrosome separation functions, the duplicated Tribolium and Acyrthosiphon arm paralogs offer new inroads for context-specific analyses of β-Catenin. Our data also revealed the conservation of a C-terminally truncated Arm isoform in both singleton and duplicated homologs, suggesting an as yet unexplored role in Wnt signaling.

Interaction of Sp1 zinc finger with transport factor in the nuclear localization of transcription factor Sp1

Transcription factor Sp1 is localized in the nucleus and regulates the expression of many cellular genes, but the nuclear transport mechanism of Sp1 is not well understood. In this study, we revealed that GST-fused Sp1 protein bound to endogenous importin α in HeLa cells via the Sp1 zinc finger domains, which comprise the DNA binding domain of Sp1. It was found that the Sp1 zinc finger domains directly interacted with a wide range of importin α including the armadillo (arm) repeat domain and the C-terminal acidic domain. Furthermore, it turned out that all three zinc fingers of Sp1 are essential for binding to importin α. Taken together, these results suggest that the Sp1 zinc finger domains play an essential role as a NLS and Sp1 can be transported into the nucleus in an importin-dependent manner even though it possesses no classical NLSs.

The Terminal Region of β-Catenin Promotes Stability by Shielding the Armadillo Repeats from the Axin-scaffold Destruction Complex

Post-translational stabilization of beta-catenin is a key step in Wnt signaling, but the features of beta-catenin required for stabilization are incompletely understood. We show that forms of beta-catenin lacking the unstructured C-terminal domain (CTD) show faster turnover than full-length or minimally truncated beta-catenins. Mutants that exhibit faster turnover show enhanced association with axin in co-transfected cells, and excess CTD polypeptide can compete binding of the beta-catenin armadillo (arm) repeat domain to axin in vitro, indicating that the CTD may restrict beta-catenin binding to the axin-scaffold complex. Fluorescent resonance energy transmission (FRET) analysis of cyan fluorescent protein (CFP)-arm-CTD-yellow fluorescent protein beta-catenin reveals that the CTD of beta-catenin can become spatially close to the N-terminal arm repeat region of beta-catenin. FRET activity is strongly diminished by the coexpression of beta-catenin binding partners, indicating that an unliganded groove is absolutely required for an orientation that allows FRET. Amino acids 733-759 are critical for beta-catenin FRET activity and stability. These data indicate that an N-terminal orientation of the CTD is required for beta-catenin stabilization and suggest a model where the CTD extends toward the N-terminal arm repeats, shielding these repeats from the beta-catenin destruction complex.

LFR, which encodes a novel nuclear-localized Armadillo-repeat protein, affects multiple developmental processes in the aerial organs in Arabidopsis

The Armadillo (ARM)-repeat domain is a 42-amino acid protein-protein interaction motif present in many eukaryotic proteins. ARM-repeat proteins function in many cellular processes, including cytoskeletal regulation, nucleo-cytoplasmic trafficking, and transcriptional regulation. More than 100 genes encoding ARM-repeat proteins are predicted to exist in the Arabidopsis thaliana genome; however, most of them have unknown biological functions. Using map-based cloning, we isolated a novel recessive loss-of-function mutant, lfr-1, with developmental and morphological defects at the vegetative stage in the cotyledons and true leaves, and during the reproductive phase in the flowers and siliques. Complementation experiments and an analysis of the T-DNA insertion mutant lfr-2 revealed that LFR was responsible for all of the mutant phenotypes. LFR encodes a protein with three putative ARM-repeat domains that tends to cluster in the nucleus as discrete rounded speckles. LFR was broadly expressed while LFR was largely concentrated in the stem apex and root tip. Our data suggest that LFR is a novel nuclear-localized ARM-repeat protein that functions in leaf and flower development in Arabidopsis.

Novel expression of importin α homologue in marine teleost, Pagrus major

Importin α proteins are critical modulators of the classical nuclear protein import pathway. Although the physiological roles of importin α have been extensively studied in invertebrates and mammals, very little is known about their counterparts in lower vertebrates. In this study, to elucidate the roles of importin α in a teleost species, we isolated and characterized red seabream ( Pagrus major) importin α cDNA derived from ovary and found changes in the mRNA levels of importin α in male and female red seabream during sexual maturation. The 1846-bp cDNA encodes a 520 amino acid protein that includes the importin β-binding domain, a short acidic domain, and an armadillo (arm) repeat domain. Northern blot analysis and reverse transcription-polymerase chain reaction (RT-PCR) showed transcription of red seabream importin α in testis and ovary but not in the other tissues. The importin α mRNA levels in males increase in association with testicular development, whereas those in females remain high throughout sexual maturation. These findings suggest that red seabream ovary-derived importin α may be controlled in a tissue-specific manner and may perform unique functions in the gonad in addition to its involvement in nuclear transport.