Conserved Ser residues in the basic region of the bZIP-type transcription factor HBP-1a(17): importance in DNA binding and possible targets for phosphorylation.
HBP-1a(17) is representative of a group of plant bZIP-type transcription factors which includes HBP-1a proteins and G-box-binding factors. We found kinase activity in wheat nuclear extract that phosphorylated HBP-1a(17). Experiments using recombinant HBP-1a(17) derivatives as substrates revealed that all three of the Ser residues in the basic region, Ser-261, Ser-265, and Ser-269, were phosphorylated in a Ca(2+)-stimulated manner. DNA-binding analysis of mutants with a Ser-to-Glu change, prepared to mimic the phosphorylated proteins, indicated that introduction of a negative charge at position 265 or 269 prevents HBP-1a(17) from binding DNA not only in the homodimer of mutants but also in heterodimers with a wild-type protein. It is therefore suggested that the phosphorylation regulates the function of HBP-1a(17) at least at the level of DNA binding. Since Ser-265 and Ser-269 are highly conserved among the plant bZIP-type factors known to date, a common Ca(2+)-mediated regulatory mechanism may exert an effect on the bZIP-type factors through phosphorylation of these conserved Ser residues.
Meshi
T
T
Department of Botany, Graduate School of Science, Kyoto University, Japan.
Moda
I
I
Minami
M
M
Okanami
M
M
Iwabuchi
M
M
D000595:Amino Acid Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D001665:Binding Sites; D002118:Calcium / Q000494:pharmacology; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D003001:Cloning, Molecular; D017124:Conserved Sequence; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D016350:Leucine Zippers; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009687:Nuclear Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D010449:Peptide Mapping; D010748:Phosphopeptides / Q000737:chemistry; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism; D017354:Point Mutation; D016133:Polymerase Chain Reaction; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis; D011994:Recombinant Proteins / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D012694:Serine; D014157:Transcription Factors / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D014908:Triticum / Q000378:metabolism*; D001616:beta-Galactosidase / Q000096:biosynthesis
D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; C068756:HBP-1a protein, Triticum aestivum; D009687:Nuclear Proteins; D010748:Phosphopeptides; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; D010768:Phosphoserine; D012694:Serine; D001616:beta-Galactosidase; D002118:Calcium