SPGCF1, A SEA-URCHIN EMBRYO DNA-BINDING PROTEIN, EXISTS AS 5 NESTED VARIANTS ENCODED BY A SINGLE MESSENGER-RNA

Several Strongylocentrotus purpuratus gene cis-regulatory regions cont ain asymmetric C-4 sequences which are core elements of target sites f or a specific DNA-protein interaction. Blastula stage nuclear extract contains five proteins which specifically bind to these target sites, resulting in a characteristic pattern of complexes in gel mobility shi ft assays. We used automated affinity chromatography to purify a prote in which binds to these sites and have isolated the corresponding cDNA . This protein, SpGCF1, is a novel sea urchin DNA-binding protein with no overall homology to proteins reported in the databases currently a vailable. The DNA-binding domain of this protein was identified by a d eletion analysis. As demonstrated both for protein translated in vitro and for bacterial protein expressed from a cDNA clone, a single SpGCF 1 mRNA serves as a template for the synthesis of five DNA-binding poly peptides. We show that these five polypeptides are most likely produce d by differential usage of a nested set of AUG start codons in the SpG CF1 cDNA and thus contain variable amounts of a proline-rich N-termina l domain. Since proline-rich regions often serve as transcriptional ac tivation domains, the five SpGCF1 proteins apparently possess differen t ''activation potentials.'' (C) 1995 Academic Press, Inc.