Tandem Affinity Purification Approach Research Articles

WWP2 is an E3 ubiquitin ligase for PTEN

PTEN, a lipid phosphatase, is one of the most frequently mutated tumour suppressors in human cancer. Several recent studies have highlighted the importance of ubiquitylation in regulating PTEN tumour-suppressor function, but the enzymatic machinery required for PTEN ubiquitylation is not clear. In this study, by using a tandem affinity-purification approach, we have identified WWP2 (also known as atrophin-1-interacting protein 2, AIP-2) as a PTEN-interacting protein. WWP2 is an E3 ubiquitin ligase that belongs to the NEDD4-like protein family, which is involved in regulating transcription, embryonic stem-cell fate, cellular transport and T-cell activation processes. We show that WWP2 physically interacts with PTEN and mediates its degradation through a ubiquitylation-dependent pathway. Functionally, we show thatWWP2controls cellular apoptosis and is required for tumorigenicity of cells. Collectively, our results reveal a functional E3 ubiquitin ligase for PTEN that plays a vital role in tumour-cell survival.

Isolation and characterization of plant protein complexes by mass spectrometry

The components that enable cells and organisms to fulfill a plethora of chemical and physical reactions, including their ability to metabolize, replicate, repair and communicate with their environment are mostly based on the functioning of highly complex cellular machines which are to a large extent composed of proteins. With the development of MS techniques compatible with the analysis of minute amounts of biological material, it has become more and more feasible to dissect the composition and modification of these protein machineries. Indeed, new purification methods of protein complexes followed by MS analysis together with the genomic sequencing of various organisms - and in particular of crop species - now provide unforeseen insight to understand biological processes at a molecular level. We here review the current state of the art of in vivo protein complex isolation and their MS-based analytical characterization, emphasizing on the tandem affinity purification approach.

Interaction Proteomics Analysis of Polycomb Proteins Defines Distinct PRC1 Complexes in Mammalian Cells

Polycomb group (PcG) proteins maintain transcriptional repression of hundreds of genes involved in development, signaling or cancer using chromatin-based epigenetic mechanisms. Biochemical studies in Drosophila have revealed that PcG proteins associate in at least two classes of protein complexes known as Polycomb repressive complexes 1 and 2 (PRC1 and PRC2). Drosophila core PRC1 is composed of four subunits, Polycomb (Pc), Sex combs extra (Sce), Polyhomeotic (Ph), and Posterior sex combs (Psc). Each of these proteins has multiple orthologs in vertebrates classified respectively as the CBX, RING1/RNF2, PHC, and BMI1/PCGF families. Mammalian genomes encode five CBX family members (CBX2, CBX4, CBX6, CBX7, and CBX8) that are believed to have distinct biological functions. Here, we applied a tandem affinity purification (TAP) approach coupled with tandem mass spectrometry (MS/MS) methodologies in order to identify interacting partners of CBX family proteins under the same experimental conditions. Our analysis identified with high confidence about 20 proteins co-eluted with CBX2 and CBX7 tagged proteins, about 40 with CBX4, and around 60 with CBX6 and CBX8. We provide evidences that the CBX family proteins are mutually exclusive and define distinct PRC1-like protein complexes. CBX proteins also interact with different efficiencies with the other PRC1 components. Among the novel CBX interacting partners, protein kinase 2 associates with all CBX-PRC1 protein complexes, whereas 14-3-3 proteins specifically bind to CBX4. 14-3-3 protein binding to CBX4 appears to modulate the interaction between CBX4 and the BMI1/PCGF components of PRC1, but has no effect on CBX4-RING1/RNF2 interaction. Finally, we suggest that differences in CBX protein interactions would account, at least in part, for distinct subnuclear localization of the CBX family members.

Identification of cyclophilin-40-interacting proteins reveals potential cellular function of cyclophilin-40

Cyclophilin-40 (CyP40) is part of the immunophilin family and is found in Hsp90-containing protein complexes. We were interested in identifying proteins that interact with CyP40. CyP40-interacting proteins in HeLa cells were identified using the tandem affinity purification approach. Adenovirus expressing human CyP40 protein (Ad–CyP40), fused with streptavidin and calmodulin binding peptides at the N terminus, was generated. Proteins were separated on a sodium dodecyl sulfate–polyacrylamide gel electrophoresis gel after tandem affinity purification. Here 10 silver-stained protein bands that were enriched in the Ad–CyP40-infected lysate and the corresponding regions in the control lysate were excised, digested by trypsin, and identified by tandem mass spectrometric analysis. Of 11 interacting proteins that were identified, 4 (RACK1, Ku70, RPS3, and NF45) were expressed in rabbit reticulocyte lysate, bacteria, and MCF-7 cells. We confirmed that these proteins interact with CyP40. We observed that RACK1 suppressed the cobalt chloride-induced, hypoxia response element-dependent luciferase activity in MCF-7 cells but not in MCF-7 stable cells expressing approximately 10% of the cellular CyP40 content. In addition, RACK1 reduced the HIF-1α protein accumulation after cobalt chloride treatment, which was not observed when the CyP40 content was down-regulated. Collectively, we conclude that reduction of the HIF-1α protein by RACK1 is CyP40-mediated.

Purification and Characterization of an Active N -Acetylglucosaminyltransferase Enzyme Complex from Streptococci

A new family of bacterial serine-rich repeat glycoproteins can function as adhesins required for biofilm formation and pathogenesis in streptococci and staphylococci. Biogenesis of these proteins depends on a gene cluster coding for glycosyltransferases and accessory secretion proteins. Previous studies show that Fap1, a member of this family from Streptococcus parasanguinis, can be glycosylated by a protein glycosylation complex in a recombinant heterogeneous host. Here we report a tandem affinity purification (TAP) approach used to isolate and study protein complexes from native streptococci. This method demonstrated that a putative glycosyltransferase (Gtf2), which is essential for Fap1 glycosylation, readily copurified with another glycosyltransferase (Gtf1) from native S. parasanguinis. This result and the similar isolation of a homologous two-protein complex from Streptococcus pneumoniae indicate the biological relevance of the complexes to the glycosylation in streptococci. Furthermore, novel N-acetylglucosaminyltransferase activity was discovered for the complexes. Optimal activity required heterodimer formation and appears to represent a novel type of glycosylation.

HIV-1 Vpr Induces the K48-Linked Polyubiquitination and Proteasomal Degradation of Target Cellular Proteins To Activate ATR and Promote G 2 Arrest

HIV-1 viral protein R (Vpr) induces cell cycle arrest at the G(2)/M phase by a mechanism involving the activation of the DNA damage sensor ATR. We and others recently showed that Vpr performs this function by subverting the activity of the DDB1-CUL4A (VPRBP) E3 ubiquitin ligase. Vpr could thus act as a connector between the E3 ligase and an unknown cellular factor whose ubiquitination would induce G(2) arrest. While attractive, this model is based solely on the indirect observation that some mutants of Vpr retain their interaction with the E3 ligase but fail to induce G(2) arrest. Using a tandem affinity purification approach, we observed that Vpr interacts with ubiquitinated cellular proteins and that this association requires the recruitment of an active E3 ligase given that the depletion of VPRBP by RNA interference or the overexpression of a dominant negative mutant of CUL4A decreased this association. Importantly, G(2)-arrest-defective mutants of Vpr in the C-terminal putative substrate-interacting domain displayed a decreased association with ubiquitinated proteins. We also found that the inhibition of proteasomal activity increased this association and that the ubiquitin chains were at least in part constituted of classical K48 linkages. Interestingly, the inhibition of K48 polyubiquitination specifically impaired the Vpr-induced phosphorylation of H2AX, an early target of ATR, but did not affect UV-induced H2AX phosphorylation. Overall, our results provide direct evidence that the association of Vpr with the DDB1-CUL4A (VPRBP) E3 ubiquitin ligase induces the K48-linked polyubiquitination of as-yet-unknown cellular proteins, resulting in their proteasomal degradation and ultimately leading to the activation of ATR and G(2) arrest.

Biotin tagging coupled with amino acid‐coded mass tagging for efficient and precise screening of interaction proteome in mammalian cells

In mammalian cells, when tandem affinity purification approach is employed, the existence of untagged endogenous target protein and repetitive washing steps together result in overall low yield of purified/stable complexes and the loss of weakly and transiently interacting partners of biological significance. To avoid the trade-offs involving in methodological sensitivity, precision, and throughput, here we introduce an integrated method, biotin tagging coupled with amino acid-coded mass tagging, for highly sensitive and accurate screening of mammalian protein-protein interactions. Without the need of establishing a stable cell line, using a short peptide tag which could be specifically biotinylated in vivo, the biotin-tagged target/bait protein was then isolated along with its associates efficiently by streptavidin magnetic microbeads in a single step. In a pulled-down complex amino acid-coded mass tagging serves as "in-spectra" quantitative markers to distinguish those bait-specific interactors from non-specific background proteins under stringent criteria. Applying this biotin tagging coupled with amino acid-coded mass tagging approach, we first biotin-tagged in vivo a multi-functional protein family member, 14-3-3epsilon, which was expressed at close to endogenous level. Starting with approximately 20 millions of 293T cells which were significantly less than what needed for a tandem affinity purification run, 266 specific interactors of 14-3-3epsilon were identified in high confidence.

Recruitment of the Linear Ubiquitin Chain Assembly Complex Stabilizes the TNF-R1 Signaling Complex and Is Required for TNF-Mediated Gene Induction

TNF is a key inflammatory cytokine. Using a modified tandem affinity purification approach, we identified HOIL-1 and HOIP as functional components of the native TNF-R1 signaling complex (TNF-RSC). Together, they were shown to form a linear ubiquitin chain assembly complex (LUBAC) and to ubiquitylate NEMO. We show that LUBAC binds to ubiquitin chains of different linkage types and that its recruitment to the TNF-RSC is impaired in TRADD-, TRAF2-, and cIAP1/2- but not in RIP1- or NEMO-deficient MEFs. Furthermore, the E3 ligase activity of cIAPs, but not TRAF2, is required for HOIL-1 recruitment to the TNF-RSC. LUBAC enhances NEMO interaction with the TNF-RSC, stabilizes this protein complex, and is required for efficient TNF-induced activation of NF-kappaB and JNK, resulting in apoptosis inhibition. Finally, we demonstrate that sustained stability of the TNF-RSC requires LUBAC's enzymatic activity, thereby adding a third form of ubiquitin linkage to the triggering of TNF signaling by the TNF-RSC.

The histone methyltransferase SUV420H2 and Heterochromatin Proteins HP1 interact but show different dynamic behaviours

BackgroundHistone lysine methylation plays a fundamental role in chromatin organization and marks distinct chromatin regions. In particular, trimethylation at lysine 9 of histone H3 (H3K9) and at lysine 20 of histone H4 (H4K20) governed by the histone methyltransferases SUV39H1/2 and SUV420H1/2 respectively, have emerged as a hallmark of pericentric heterochromatin. Controlled chromatin organization is crucial for gene expression regulation and genome stability. Therefore, it is essential to analyze mechanisms responsible for high order chromatin packing and in particular the interplay between enzymes involved in histone modifications, such as histone methyltransferases and proteins that recognize these epigenetic marks.ResultsTo gain insights into the mechanisms of SUV420H2 recruitment at heterochromatin, we applied a tandem affinity purification approach coupled to mass spectrometry. We identified heterochromatin proteins HP1 as main interacting partners. The regions responsible for the binding were mapped to the heterochromatic targeting module of SUV420H2 and HP1 chromoshadow domain. We studied the dynamic properties of SUV420H2 and the HP1 in living cells using fluorescence recovery after photobleaching. Our results showed that HP1 proteins are highly mobile with different dynamics during the cell cycle, whereas SUV420H2 remains strongly bound to pericentric heterochromatin. An 88 amino-acids region of SUV420H2, the heterochromatic targeting module, recapitulates both, HP1 binding and strong association to heterochromatin.ConclusionFRAP experiments reveal that in contrast to HP1, SUV420H2 is strongly associated to pericentric heterochromatin. Then, the fraction of SUV420H2 captured and characterized by TAP/MS is a soluble fraction which may be in a stable association with HP1. Consequently, SUV420H2 may be recruited to heterochromatin in association with HP1, and stably maintained at its heterochromatin sites in an HP1-independent fashion.

Analysis of the protein complex associated with 14-3-3 epsilon by a deuterated-leucine labeling quantitative proteomics strategy

By using an unambiguous in vivo deuterated-leucine labeling quantitative proteomic approach, at close to the physiologically relevant level, we systematically profiled multiple proteins interacting with 14-3-3ɛ, the isoform with least characterized protein interactions in 14-3-3 family in mammalian cells. Among the 19 proteins interacting with 14-3-3ɛ identified, 6 of them including SKb1Hs, p54nrb, serine/threonine kinase 38, MEP50, 14-3-3θ and cofilin 2 were the previously unknown interacting partners with 14-3-3ɛ. The newly identified interactor cofilin 2 was also validated in co-transfection and co-immunoprecipitation. In contrast, with the same stringent criteria only three known partners were identified by conventional tandem affinity purification (TAP) approach. Therefore the ‘in-spectra’ quantitative marker of deuterated-leucine assisted to precisely identify those genuine interacting partners with minimum requirement of validation using other molecular approaches.

Distinct isocomplexes of the TRAPP trafficking factor coexist inside human cells

The transport protein particle (TRAPP) complex is required for proper vesicular transport from the ER to the Golgi. The composition of yeast TRAPP is well characterized, but the organization of mammalian TRAPP complex remains elusive. Using a tandem affinity purification (TAP) approach, we provide first experimental proof for the association of NIBP (NIK/IKKβ binding protein) with Bet3 and find two human paralogs of Trs33 (A and B) associated with Bet3. Interaction studies and gel filtration analysis reveal that both proteins are part of human TRAPP and might mark two distinct isocomplexes that exert different functions in the regulation of ER-to-Golgi traffic. Structured summaryMINT-6784845:Bet3 (uniprotkb:O43617) physically interacts (MI:0218) with Trs33B (uniprotkb:Q86SZ2) by anti bait coimmunoprecipitation (MI:0006)MINT-6785053:Trs33B (uniprotkb:Q86SZ2) physically interacts (MI:0218) with Bet3 (uniprotkb:O43617) and Sedl (uniprotkb:O14582) by anti bait coimmunoprecipitation (MI:0006)MINT-6784856:Bet3 (uniprotkb:O43617) physically interacts (MI:0218) with Trs33A2 (uniprotkb:O75865-2) by anti bait coimmunoprecipitation (MI:0006)MINT-6785038:Trs33A1 (uniprotkb:O75865-2) physically interacts (MI:0218) with Sedl (uniprotkb:O14582) and Bet3 (uniprotkb:O43617) by anti bait coimmunoprecipitation (MI:0006)MINT-6784879:Bet3 (uniprotkb:O43617) physically interacts (MI:0218) with NIBP (uniprotkb:Q96Q05) by tandem affinity purification (MI:0676)MINT-6785068:Trs33B (uniprotkb:Q86SZ2), Trs33A2 (uniprotkb:O75865-2) and Bet3 (uniprotkb:O43617) colocalize (MI:0403) by molecular sieving (MI:0071)MINT-6785415:Bet3 (uniprotkb:O43617) physically interacts (MI:0218) with Trs33A1 (uniprotkb:O75865) by anti bait coimmunoprecipitation (MI:0006)

Boosting tandem affinity purification of plant protein complexes

Protein-interaction mapping based on the tandem affinity purification (TAP) approach has been successfully established for several systems, such as yeast and mammalian cells. However, relatively few protein complex purifications have been reported for plants. Here, we highlight solutions for the pitfalls and propose a major breakthrough in the quest for a better TAP tag in plants.

Analysis of the interaction of influenza virus polymerase complex with human cell factors

The influenza virus polymerase is formed by the PB1, PB2 and PA subunits and is required for virus transcription and replication in the nucleus of infected cells. Here we present the characterisation of the complexes formed intracellularly by the influenza polymerase in human cells. The virus polymerase was expressed by cotransfection of the polymerase subunits cDNAs, one of which fused to the tandem-affinity purification (TAP) tag. The intracellular complexes were purified by the TAP approach, which involves IgG-Sepharose and calmodulin-agarose chromatography, under very mild conditions. The purified complexes contained the heterotrimeric polymerase and a series of associated proteins that were not apparent in purifications of untagged polymerase used as a control. Several influenza polymerase-associated proteins were identified by MALDI-MS and their presence in purified polymerase-containing complexes were verified by Western blot. Their relevance for influenza infection was established by colocalisation with virus ribonucleoproteins in human infected cells. Most of the associated human factors were nuclear proteins involved in cellular RNA synthesis, modification and nucleo-cytoplasmic export, but some were cytosolic proteins involved in translation and transport. The interactions recognised in this proteomic approach suggest that the influenza polymerase might be involved in steps of the infection cycle other than RNA replication and transcription.

Characterization of Ire1 in the yeast Yarrowia lipolytica reveals an important role for the Sls1 nucleotide exchange factor in unfolded protein response regulation

Following endoplasmic reticulum (ER) stress, eukaryotic cells trigger a conserved signal transduction pathway called the unfolded protein response (UPR) that regulates the ER's capacity to perform protein folding according to cellular demand. In Saccharomyces cerevisiae, the UPR is initiated by Ire1, a type I transmembrane serine/threonine kinase/endoribonuclease, that senses unfolded protein levels within the ER in collaboration with the ER Hsp70-family member, BiP/Kar2. Here, we report on the characterization of the Yarrowia lipolytica Ire1 ortholog. Our results show that Sls1, a nucleotide exchange factor for BiP, has important functions in regulating ER stress and the interaction of BiP and Ire1. They suggest that Sls1 regulates this interaction, by stimulating the conversion of BiP from the ADP-bound to the ATP-bound state, which favors its interaction with Ire1. Moreover, we identified known and new partners for Ire1 using the Tandem Affinity Purification (TAP) approach.

Oligomerization of the influenza virus polymerase complex in vivo

The influenza virus polymerase is a heterotrimer formed by the PB1, PB2 and PA subunits and is responsible for virus transcription and replication. We have expressed the virus polymerase complex by co-transfection of the subunit cDNAs, one of which was tandem affinity purification (TAP)-tagged, into human cells. The intracellular polymerase complexes were purified by the TAP approach, involving two affinity chromatography steps, IgG-Sepharose and calmodulin-agarose. Gel-filtration analysis indicated that, although most of the purified polymerase behaved as a heterotrimer, a significant proportion of the purified material migrated as polymerase dimers, trimers and higher oligomers. Co-purification of polymerase complexes alternatively tagged in the same subunit confirmed that the polymerase complex might form oligomers intracellularly. The implications of this observation for virus infection are discussed.

An optimized protocol for protein purification in cultured mammalian cells using a tandem affinity purification approach

This protocol describes a method that we developed to adapt the tandem affinity purification (TAP) approach for use in mammalian cells. The protocol involves fusing a protein of interest with a tandem tag consisting of two FLAG tags (FF) followed by two protein-A immunoglobulin G (IgG) binding domains (ZZ). The protocol improves upon previously published TAP approaches by employing FLAG in place of calmodulin binding peptide (CBP) with resulting higher recovery during purification. In addition, we use a bicistronic expression system that ensures recovery of stably transfected cell lines expressing easily detectable levels of the protein of interest. A method is also presented for generating cytoplasmic and nuclear extracts, which extends use of this protocol to identify protein-protein interactions occurring specifically in the cytoplasm or nucleus. This protocol facilitates the preparation of partially purified recombinant protein and identification of protein-protein interactions in mammalian cell culture models. The protocol can be completed in 34 h.

Transgenic Mouse Proteomics Identifies New 14-3-3-associated Proteins Involved in Cytoskeletal Rearrangements and Cell Signaling

Identification of protein-protein interactions is crucial for unraveling cellular processes and biochemical mechanisms of signal transduction. Here we describe, for the first time, the application of the tandem affinity purification (TAP) and LC-MS method to the characterization of protein complexes from transgenic mice. The TAP strategy developed in transgenic mice allows the emplacement of complexes in their physiological environment in contact with proteins that might only be specifically expressed in certain tissues while simultaneously ensuring the right stoichiometry of the TAP protein versus their binding partners and represents a novelty in proteomics approaches used so far. Mouse lines expressing TAP-tagged 14-3-3zeta protein were generated, and protein interactions were determined. 14-3-3 proteins are general regulators of cell signaling and represent up to 1% of the total brain protein. This study allowed the identification of almost 40 novel 14-3-3zeta-binding proteins. Biochemical and functional characterization of some of these interactions revealed new mechanisms of action of 14-3-3zeta in several signaling pathways, such as glutamate receptor signaling via binding to homer homolog 3 (Homer 3) and in cytoskeletal rearrangements and spine morphogenesis by binding and regulating the activity of the signaling complex formed by G protein-coupled receptor kinase-interactor 1 (GIT1) and p21-activated kinase-interacting exchange factor beta (betaPIX).

NIR is a novel INHAT repressor that modulates the transcriptional activity of p53

Most transcriptional repression pathways depend on the targeted deacetylation of histone tails. In this report, we characterize NIR, a novel transcriptional corepressor with inhibitor of histone acetyltransferase (INHAT) activity. NIR (Novel INHAT Repressor) is ubiquitously expressed throughout embryonic development and adulthood. NIR is a potent transcriptional corepressor that is not blocked by histone deacetylase inhibitors and is capable of silencing both basal and activator-driven transcription. NIR directly binds to nucleosomes and core histones and prevents acetylation by histone acetyltransferases, thus acting as a bona fide INHAT. Using a tandem affinity purification approach, we identified the tumor suppressor p53 as a NIR-interacting partner. Association of p53 and NIR was verified in vitro and in vivo. Upon recruitment by p53, NIR represses transcription of both p53-dependent reporters and endogenous target genes. Knock-down of NIR by RNA interference significantly enhances histone acetylation at p53-regulated promoters. Moreover, p53-dependent apoptosis is robustly increased upon depletion of NIR. In summary, our findings describe NIR as a novel INHAT that plays an important role in the control of p53 function.

RhoF GTPase Transcription Is Upregulated in Germinal Center B-Cells, Shows Altered Expression in Malignant B-Cells, and Interacts with the ATM Pathway.

Follicular lymphoma (FL) is the most common low-grade B-cell non Hodgkin lymphoma in the Western hemisphere. A significant proportion of FL undergo histologic transformation to diffuse large B-cell lymphoma (DLBCL). Using cDNA microarray analysis, we identified an expressed sequence tag GI#10952525 consistently differentially expressed in transformed follicular lymphomas (tFL). This was characterized as RhoF, a novel member of the Rho family. Rho GTPases play central roles in cytoskeletal dynamics, cell-cell interactions, and intracellular signaling pathways involved in migration, proliferation and survival. Dysregulation of Rho proteins are key events implicated in tumorigenesis.To define the role of RhoF in lymphocyte physiology and lymphoma transformation, we assessed its expression across phenotypically defined lymphocyte subpopulations, using quantitative real-time PCR. We determined relative RhoF levels in immunomagnetic bead purified normal lymphoid subpopulations [naïve B-cells, memory B-cells, germinal center B-cells and T-cells], reactive lymphoid tissues (n=5), cell lines [derived from t(14;18) tFL (n =3), de novo DLBCL (n=7), and T-cell malignancy (n=3)] and tissue from primary human lymphoid neoplasms [FL (n=5), de novo DLBCL (n=5), tFL (n=5), CLL/SLL (n=4), anaplastic large cell lymphoma (n=8), mantle cell lymphoma (n=5), and T-cell acute lymphoblastic leukemia (n=5)]. RhoF was expressed at significantly higher levels in B-cells relative to T-cells. We saw this pattern in purified lymphocyte subpopulations, in cell lines, and in primary lymphoma tissue samples. Notably, we detected elevated levels of RhoF transcript in B-cells of germinal center (GC) origin, both in the reactive and neoplastic samples of GC-derived B-cells. The highest transcriptional levels of RhoF were in malignant B-cells of GC origin; both in heterogeneous primary tissue samples and in homogeneous tissue culture preparations.To investigate its functional role, we cloned RhoF into a vector coding for a C-terminal polyhistidine- and V5 epitope-tag. We expressed the constructs in HEK 293T cells, and purified the RhoF-containing complexes using a tandem affinity purification approach. We ran cell lysates through a nickel column; non-interacting proteins were washed off under native conditions and the bound RhoF complexes eluted with imidazole. Eluate was immunoprecipitated with sepharose-bound anti-V5 antibody. Immunoprecipitated complexes were denatured and resolved by 1D-PAGE. Unique bands representing RhoF interacting proteins were isolated and enzymatically cleaved with trypsin. Resultant peptides underwent liquid chromatography and tandem mass spectrometry. Data were searched against the NCBI nr.FASTA nonredundant protein database using the SEQUEST algorithm and false positive rates determined with INTERACT and ProteinProphet. Among several putative RhoF interactors, we identified ATM as an important RhoF binding partner.In conclusion, our demonstration of the differential expression of RhoF in GC-derived cells and its upregulation in tFL provide evidence for a connection between the role of this novel protein in B-cell development and malignancy. In addition, evidence of an association between RhoF and ATM may provide a link between DNA repair, cell cycle control and morphological dynamics.

A critical and integrated view of the yeast interactome

Global studies of protein–protein interactions are crucial to both elucidating gene function and producing an integrated view of the workings of living cells. High-throughput studies of the yeast interactome have been performed using both genetic and biochemical screens. Despite their size, the overlap between these experimental datasets is very limited. This could be due to each approach sampling only a small fraction of the total interactome. Alternatively, a large proportion of the data from these screens may represent false-positive interactions. We have used the Genome Information Management System (GIMS) to integrate interactome datasets with transcriptome and protein annotation data and have found significant evidence that the proportion of false-positive results is high. Not all high-throughput datasets are similarly contaminated, and the tandem affinity purification (TAP) approach appears to yield a high proportion of reliable interactions for which corroborating evidence is available. From our integrative analyses, we have generated a set of verified interactome data for yeast.