Wheat Histone Genes Research Articles

S phase-specific DNA-binding proteins interacting with the Hex and Oct motifs in type I element of the wheat histone H3 promoter.

The type I element (CCACGTCANCGATCCGCG), consisting of the Hex motif (CCACGTCA) and the reverse-oriented Oct motif (GATCCGCG), is necessary and sufficient to confer the S phase-specific transcription of the wheat histone H3 (TH012) gene. The transcriptional regulation via the type I element is thought to occur through interactions between transcription factors which bind specifically to the Hex and Oct motifs. Here we report S phase-specific DNA-binding proteins interacting with the type I element in partially synchronized wheat cultured cells. Hex motif-binding proteins found here resembled HBP-1a, as reported previously in terms of DNA-binding specificity. DNA-binding activities of the HBP-1a-like proteins were modulated by phosphorylation/dephosphorylation. In the electrophoretic mobility shift assay of the wheat nuclear extract, we also found three Oct motif-specific binding proteins, named OBRF (octamer-binding regulatory factor)-1, -2 and -3. One of the HBP-1a-like proteins and OBRF-1 appeared predominantly at the S phase. Thus, it was supposed that these two factors play a crucial role in the S phase-specific regulation of wheat histone gene expression.

A zinc-finger-type transcription factor WZF-1 that binds to a novel cis-acting element of histone gene promoters represses its own promoter.

WZF-1 is a zinc-finger protein which binds to the wheat histone gene promoter. Southwestern-binding analyses revealed that it bound a CACTC sequence, a novel positive cis-acting element. The activity of WZF-1 gene promoter, containing six CACTC sequences, was markedly reduced when WZF-1 was co-expressed, suggesting that WZF-1 is a transcriptional repressor.

The putative zinc‐finger protein WZF1 interacts with a cis‐acting element of wheat histone genes

A nonamer motif (CATCCAACG) that is one of the cis-acting elements identified in the proximal promoter region of some wheat histone genes is included in the region that interacts with the wheat DNA-binding protein, HBP (histone gene-binding protein)-2. To obtain structural and functional information about this DNA-binding protein, we attempted to isolate a cDNA clone encoding HBP-2 on the basis of its ability to bind to a nonamer-containing 38-bp DNA fragment. Southwestern screening of a wheat cDNA library with concatenated 38-residue oligonucleotides as the probe produced one candidate clone. Nucleotide sequence analyses of this cDNA clone and the corresponding genomic clone showed that the protein deduced from the nucleotide sequence consisted of 261 amino acids and contained a set of zinc-finger motifs similar to those found in many eukaryotic transcription factors. The protein, named WZF1 (wheat zinc-finger protein 1), which was expressed from the cDNA in Escherichia coli cells, bound specifically and metal-ion-dependently to the nonamer-containing oligonucleotide. The WZF1 mRNA was highly expressed in the root apexes of wheat seedlings, but less so in the proximal portion of young leaves; whereas, histone H3 mRNA was highly expressed in both tissues. The expression patterns of the WZF1 and histone H3 genes in the early stages of germination differed, expression of the WZF1 gene being almost constant but not that of the H3 gene. The relationship of WZF1 and HBP-2 and the possible role of WZF1 in the histone gene expression were discussed.

Coordinate gene expression of five subclass histones and the putative transcription factors, HBP-1a and HBP-1b, of histone genes in wheat.

The expression of genes encoding five histones (H1, H2A, H2B, H3 and H4) and the putative transcription factors HBP-1a (17) and HBP-1b (c38) was examined during early germination and in various tissues of young wheat seedlings. The steady-state levels of core histone (H2A, H2B, H3 and H4) mRNAs were coordinately cell cycle-dependent and paralleled the rate of DNA synthesis during early germination, whereas the expression pattern of the linker histone (H1) genes differed. The five subclass histone genes were actively expressed in the meristematic tissues of young seedlings. Moreover, H1 genes were expressed in leaves that consist mostly of non-proliferating cells, in which core histone genes showed little expression. Quantitative alterations to the mRNAs of the putative transcription factors HBP-1a (17) and HBP-1b (c38) of wheat histone genes were similar to those of the core histone mRNAs, suggesting that both factors function in the cell cycle-dependent expression of wheat core histone genes.

Regulation of wheat histone gene expression

Abstract A chimeric gene composed of the wheat histone H3 promoter and the coding region of bacterial β‐glucuronidase (GUS) gene is expressed in a cell cycle‐dependent manner in transformed cultured rice cells. The same gene also is expressed in meristematic tissues such as root tips and in nondividing tissues such as the anther wall and pistil of transgenic rice plants. All these types of expression are conferred by the region from —185 to +57 in the promoter. Within this region, at least three types of cw‐acting elements are present: hexamer (ACGTCA), octamer (CGCGGATC), and nonamer (CATCCAACG). These motifs are the most probable candidates for the cis‐acting elements that control cell cycle‐dependent and/or tissue‐specific expression of histone genes. The hexamer motif interacts specifically with the wheat nuclear DNA binding proteins HBP‐la and HBP‐lb, and the nonamer motif interacts with HBP‐2. Analysis of the primary structures of the cDNAs encoding HBP‐la and HBP‐lb established that both proteins a...

Regulation of Wheat Histone Gene Expression

Regulation of Wheat Histone Gene Expression

Partial Purification and Characterization of Two Transcription Factors, HBP-la and HBP-lb, Specific for a <italic>cis</italic>-Acting Element, ACGTCA, of Wheat Histone Genes

Partial Purification and Characterization of Two Transcription Factors, HBP-la and HBP-lb, Specific for a <italic>cis</italic>-Acting Element, ACGTCA, of Wheat Histone Genes

Leucine-zipper type transcription factors of wheat

Sequence specific DNA-binding proteins play a significant role in transcriptional regulation. Wheat DNA-binding proteins, HBP-1a and HBP-1b, bind to the hexamer sequence of wheat histone gene promoters. Structural analyses of cDNAs encoding these proteins show that they belong to a leucine zipper class of transcription factors. They form homodimers but do not heterodimers between them. Although the hexamer sequence or its homologues exist in several plant genes, HBP-1a and -1b exhibited the highest binding affinity to the hexamer sequence in the histene gene promoters, suggest-ing that both DNA-binding proteins are involved in transcriptional regulation of wheat histone genes.

HBP-1a and HBP-1b: leucine zipper-type transcription factors of wheat.

Wheat transcription factors HBP-1a and HBP-1b bind to the hexamer motif, ACGTCA, of wheat histone gene promoters. HBP-1b also binds to the hexamer motif in the promoter of the 35S RNA gene of cauliflower mosaic virus, whereas HBP-1a does not. A cDNA clone encoding HBP-1b was isolated on the basis of its binding specificity to the hexamer motif. The deduced amino acid sequence indicates that HBP-1b, like HBP-1a, belongs to a leucine zipper class of transcription factors. Mutational analyses of the HBP-1a and -1b encoded cDNAs revealed that truncated polypeptides containing the leucine zipper and basic regions are sufficient for DNA binding. HBP-1a and -1b form homodimers, as expected from earlier studies on this class of transcription factors, but did not form heterodimers. Although the hexamer motif or its homologs exist in several plant genes, HBP-1a and -1b exhibited the highest binding affinity to the hexamer motif in the histone promoters, suggesting that both DNA binding proteins are involved in transcriptional regulation of wheat histone genes.

Sequence-specific single-strand DNA-binding proteins that interact with the regulatory regions of wheat histone H3 and H4 genes

We identified two novel DNA-binding proteins, ssDBP-1 and ssDBP-2, in wheat germ nuclear extract that interact with the proximal sequences of the promoter regions of the wheat histone H3 and H4 genes. Mobility shift and methylation interference assays have demonstrated that these factors specifically bind to the single-strand DNA which partially overlaps the hexamer and octamer cis-elements of the H3 promoter. Both proteins are distinguishable from HBP-1a and HBP-1b which specifically bind to the H3 hexamer sequence. These ssDNA-binding proteins are supposed to regulate the transcription of the wheat histone genes.

Cell cycle‐regulated gene expression in transgenic plant cells

A majority of histone genes are expressed in the S phase during the cell cycle. Using the gene expression system of transformed sunflower cells into which wheat histone H3 gene was introduced by the Ti-plasmid gene transfer technique, we determined three cis-acting control sequences (hexameric, octameric, and nonameric motifs) which seemed to confer the S-phase-specific transcription of wheat histone genes. Furthermore, as candidates for regulatory transcription factors, three nuclear DNA-binding proteins HBP-1a, HBP-1b, and HBP-2 that interact with the hexameric and nonameric motifs were identified. The structural analysis of the cDNA of HBP-1a revealed that a nuclear protein has the leucine-zipper structure and a DNA-binding motif. The hexameric motif in the H3 gene was also seen in cauliflower mosaic virus 35S (CaMV 35S) promoter and shown to function as a regulatory element of this promoter. The wheat HBP-1b can interact with the hexameric motif of the CaMV 35S promoter. Much attention has been paid to the significance of the hexameric sequences within the H3 and CaMV 35S promoters and the DNA-binding proteins HBP-1a and HBP-1b.

Function of the hexameric sequence in the cauliflower mosaic virus 35S RNA promoter region

The hexameric sequence ACGTCA functions in transcriptional regulation of wheat histone genes. The cauliflower mosaic virus (CaMV) 35S RNA promoter has the same hexameric sequence, and mutation analyses confirmed that the hexamer contributed greatly to transcription from the 35S promoter when a test gene with this promoter was introduced into sunflower cells. Electrophoretic mobility shift assays revealed the existence of a nuclear protein(s) in sunflower cells which is homologous to the HBP-1b that has been identified as binding to the 35S promoter in wheat. These results provide evidence of the involvement of the hexameric sequence and the HBP-1b-like DNA binding protein(s) in transcription from the 35S promoter.

Specific Interaction of Nuclear Protein HBP-1 with the Conserved Hexameric Sequence ACGTCA in the Regulatory Region of Wheat Histone Genes

The plant histone genes sequenced so far have conserved hexameric (ACGTCA) and octameric (CGCGGATC) sequences in their 5'-flanking regions. We proviously showed that the nuclear protein HPB-1 binds to the hexameric sequence of wheat histone H3 and H4 genes. Here we report several lines of evidence that confirm the existance of this DNA-binding protein and describe the results of our analysis of its binding properties

DNA-binding protein(s) interacts with a conserved nonameric sequence in the upstream regions of wheat histone genes

A nuclear protein(s), HBP-2, that binds to the upstream region of the wheat histone H4 gene was identified from a fractionated nuclear extract of wheat germ by DNase I footprinting. The DNase I-protected region contained the conserved nonameric motif, CATCCAACG. Cross-competition experiments that used the mobility shift assay showed that this nuclear protein(s) binds specifically to the upstream sequence that has been postulated to be a cis element of the wheat H3 gene. Our findings suggest that this DNA-binding protein(s) may be a trans-acting factor in the regulation of the transcription of wheat histone genes.

Nuclear protein(s) binding to the conserved DNA hexameric sequence postulated to regulate transcription of wheat histone genes

Nuclear protein(s) that specifically bind(s) to the upstream hexamer motif, ACGTCA, of wheat histone H3 and H4 genes has (have) been identified. Sequences homologous to this hexamer are found to be conserved in the upstream region of not only wheat histone genes but also other plant and animal histone genes. This suggests a possible role(s) for the hexamer and the nuclear protein(s) in the transcriptional regulation of the wheat histone genes. This hexamer is homologous to the upstream core sequence, TGACGTCA, which is highly conserved in some animal genes whose expression is regulated by cAMP.

An Accurate Transcription of Wheat Histone Genes in Sunflower Cells

An Accurate Transcription of Wheat Histone Genes in Sunflower Cells

Characteristic Sequences in the 3′ Flanking Region of Wheat Histone Genes

The 3′ flanking sequences of the coding regions of three wheat histone genes (one H3 and two H4 genes) were examined in an attempt to find signal sequences involved in regulating the transcription of the histone genes. A characteristic sequence, 5′(T)n(G)m-TG-AT3′, was found in the vicinity of the region at which the 3′ end of the wheat histone mRNA was mapped. This sequence was different from the polyadenylation signal or dyad symmetry structure that is common to animal histone genes.