[Thermal denaturation and nuclease degradation of complexes of stellins A and B with DNA].

The soluble complexes of stellins A and B-protamines from Acipenser stellatus-with DNA were obtained by direct mixing in 2,5.10(-4) M EDTA, pH 8,0. The differential curves of melting of the complexes reveal two transitions at Tmelt.1=49+/-1 degree and Tmelt.2=90+/-1 degree, corresponding to melting of DNA regions of free and protamine-bound DNA regions. The number of amino acid residues per one nucleotide in the protein-binding sites of DNA is 1,30 and 1,22 for the stellin A- and stellin B-DNA complexes, respectively. It was demonstrated that under denaturation the DNA filaments do not break apart completely. Data from the analysis of products of the complexes hydrolysis by DNAse I allowed to postulate a selective binding of the protamines to the AT-pairs of DNA. This assumption was confirmed by changes in the melting curves under different protein/DNA ratios.