HALF-1, a bZIP-type protein, interacting with the wheat transcription factor HBP-1a contains a novel transcriptional activation domain.
BACKGROUND
Nuclear factors bind to cis-acting elements and mediate transcriptional regulation through protein-protein interactions with other factors. The bZIP-type wheat nuclear protein HBP-1a(17) is a putative transcriptional activator specifically binding to the Hex (ccACGTCA) and G-box (CCACGTGG) motifs, which are often found in the cis-acting elements critical for various responses in plants.


RESULTS
In order to investigate the mechanisms for gene expression mediated via the Hex and G-box motifs, we attempted to isolate proteins interacting with HBP-1a(17) based on protein-protein interactions. A cDNA expression library from wheat seedlings was screened with 32P-labelled HBP-1a(17), and a bZIP-type protein, termed HALF-1 (HBP-1-associated leucine-zipper factor-1), was isolated. GST-pulldown assay, yeast two-hybrid system and EMSA showed that HALF-1 and HBP-1a(17) interact with each other through their leucine-zipper regions. Dissection experiments showed that HALF-1 has at least one potential trans-activation domain which includes a nine amino acid motif conserved between several plant bZIP-type proteins. This motif, named GCB (GBF-conserved box; consensus, NLNIGMDXW), activated the expression of a reporter gene, when fused to the GAL4 DNA-binding domain. The corresponding region of Arabidopsis GBF1 also stimulated transcription. However, the trans-activation domain of HALF-1 did not function in yeast.


CONCLUSIONS
We identified a novel trans-activation domain which contains the GCB motif conserved among plant bZIP-type factors. The trans-activation appears to be mediated by interaction between the GCB motif and a factor conserved in plants.
Okanami
M
M
Department of Botany, Faculty of Science, Kyoto University, Japan.
Meshi
T
T
Tamai
H
H
Iwabuchi
M
M
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics / Q000378:metabolism; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D003001:Cloning, Molecular; D017124:Conserved Sequence; D018076:DNA, Complementary / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D051790:G-Box Binding Factors; D016350:Leucine Zippers; D008969:Molecular Sequence Data; D009687:Nuclear Proteins / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D014908:Triticum / Q000235:genetics / Q000378:metabolism
D050976:Basic-Leucine Zipper Transcription Factors; D018076:DNA, Complementary; D018744:DNA, Plant; D004268:DNA-Binding Proteins; D051790:G-Box Binding Factors; C068756:HBP-1a protein, Triticum aestivum; D009687:Nuclear Proteins; D010940:Plant Proteins; D015534:Trans-Activators; D014157:Transcription Factors