[Protein factor from regenerating rat liver destabilizing secondary DNA structure].

In DNA preparations isolated from regenerating rat liver 22 hours after partial hepatectomy, i.e. at the period of the most intensive DNA synthesis a "Denaturating Protein Factor" (DPF) tightly bound to DNA was found. Isolated protein fraction with a molecular weight of 6500 dalton was found to be homogenous upon SDS-polyacrylamide electrophoresis. The degree of destabilisation of DNA was estimated by its reaction with water-soluble [14C]CME-carbodiimide which modifies selectively guanine and thymine residues only in the denatured DNA regions. Pronase treated DPF loses its DNA-denaturing capacity. Pronase treatment of DNA--DPF complex restores native DNA structure. DPF from rat liver was able to denature DNA from calf thymus and bacteriophage T7 DNA. A hypothesis is proposed that the DPF is responsible for the destabilization of DNA secondary structure in the process of replication.