[Reaction between the protein of gene 32 of phage T4 with DNA. Comparison of the properties of native protein and the product of its limited hydrolysis].

Interaction between DNA and limited hydrolysate of T4 gene 32 protein has been studied. This limited hydrolysate is obtained when 8000 dalton segment of native 32 protein is removed proteolitically, its molecular weight being 26,000 dalton. It is shown that the melting temperatures of DNA as well as that of the synthetic homopolymer poly[d(AT)] complexed with this modified protein are more than 60 degrees lower than that of pure DNA and poly[d(AT]. The secondary structure defects in DNA promote its unwinding by the modified 32 protein. As follows from the analysis of the melting curves of the modified 32 protein -- DNA complex, this protein cooperatively binds to denatured DNA. The binding constants and cooperativity parameters are found to be equal to 10(8)--10(10) M-1 AND 10(3) respectively. It is shown that the gene 32 protein in the same environmental conditions does not destabilized native DNA and poly[d(AT)].