Purification of a high-mobility-group 1 sea-urchin protein and cloning of cDNAs

The isolation of the sea urchin high-mobility-group 1 (HMG1) protein, the cloning of corresponding cDNA clones and the similarity to the human homologue are described. Sea urchin HMG1 was purified as one of the nuclear embryonic proteins which associate with an upstream regulatory element (El) of the Strongylocentrotus purpuratus (Sp) CyIIIb actin-encoding gene. Using a synthetic oligodeoxyribonucleotide (oligo) which includes the E1 cis-acting element in a DNA affinity chromatography purification, the most prominent of the binding proteins was isolated and the N terminus sequenced. cDNA clones were isolated by screening an embryonic cDNA library with a synthetic oligo derived from the amino acid (aa) sequence. Comparison of the cDNAs ORF to known proteins revealed a 50% aa identity to the mammalian HMG1 and all the structural characteristics of this group of proteins. The sea urchin protein, SpHMG1, was synthesized in bacteria, as well as translated in vitro. Binding assays carried out with the recombinant SpHMG1 protein did not produce specific in vitro complexes with E1.