The HMG-I/Y protein PF1 stimulates binding of the transcriptional activator GT-2 to the PHYA gene promoter.
The DNA-binding proteins PF1 and GT-2 are factors that bind to different functionally defined, positively acting cis-elements in the PHYA genes of oat and rice, respectively. PF1 is an HMG-I/Y protein, with its cognate cis-element being an AT-rich sequence, designated PE1, whereas GT-2 is a transcriptional activator with twin DNA binding domains that recognize a triplet of GT-boxes in a complex motif designated GTE. To further define the DNA-binding activity of PF1 and to explore potential inter-relationships between the two factors, we have performed a series of in vitro DNA-binding experiments with both PE1 and GTE target sites. The data show that, consistent with its membership of the HMG-I/Y protein family, PF1 can bend DNA when bound to PE1. In addition, PF1 can bind promiscuously, with varying affinity, to other AT-containing motifs, including GTE. When co-incubated with GT-2, PF1 enhances the specific DNA-binding activity of GT-2 toward GTE, the first report of such activity for a plant HMG-I/Y protein. This enhancement takes place without demonstrable physical contact between the two proteins, suggesting the possibility of a novel, indirect mechanism of recruitment involving DNA target-site pre-conditioning. The evidence indicates therefore that PF1 and GT-2 do not perform functionally equivalent roles in positively regulating oat and rice PHYA gene expression. However, the data suggest the possibility that PF1 may act as an architectural factor, promiscuously recognizing a spectrum of AT-containing elements in plant promoters, with the general function of catalyzing enhanced binding of conventional cognate transcriptional regulators to these elements via DNA bending.
Martínez-García
J F
JF
Department of Plant and Microbial Biology, University of California, Berkeley 94720, USA.
Quail
P H
PH
D001483:Base Sequence; D018744:DNA, Plant; D004268:DNA-Binding Proteins / Q000378:metabolism*; D006609:High Mobility Group Proteins / Q000378:metabolism*; D012275:Oryza / Q000235:genetics; D010834:Phytochrome / Q000235:genetics*; D051942:Phytochrome A; D010940:Plant Proteins; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D014157:Transcription Factors / Q000378:metabolism*
D018744:DNA, Plant; D004268:DNA-Binding Proteins; D006609:High Mobility Group Proteins; D051942:Phytochrome A; D010940:Plant Proteins; D014157:Transcription Factors; C086710:positive element factor 1 protein, Oryza sativa; D010834:Phytochrome; C077393:rice nuclear protein GT-2