PHOSPHORYLATION OF AN N-TERMINAL MOTIF ENHANCES DNA-BINDNG ACTIVITY OF THE HUMAN SRY PROTEIN

Of the several strategies that eukaryotes have evolved to modulate tra nscription factor activity, phosphorylation is regarded as one of the major mechanisms in signal-dependent transcriptional control, To concl usively demonstrate that the human sex-determining gene SRY is affecte d by such a post-translational control mechanism, we have analyzed its phosphorylation status in living cells. in the present study, we show that the cyclic AMP-dependent protein kinase (PKA) phosphorylates the human SRY protein in vitro as well as in vivo on serine residues loca ted in the N-terminal part of the protein, This phosphorylation event was shown to positively regulate SRY DNA-binding activity and to enhan ce the ability of SRY to inhibit a basal promoter activity located dow nstream of an SRY DNA-binding site concatamer. Together these results strongly support the hypothesis that human SRY is a natural substrate for PKA in vivo and that this phosphorylation significantly modulates its major activity, DNA-binding, thereby possibly altering its biologi cal function.