[Changes in the composition of nucleotide sequences in the transcriptionally active fraction of rat liver DNA during cortisol induction].

The renaturation kinetics of functionally different DNA fractions of rat liver isolated by modified phenol fractionation were studied. It was found that the transcriptionally active fraction of DNA (DNA-I), making up to approximately 20% of total DNA, is enriched with unique sequences. Under cortisol-induced DNA-dependent synthesis of RNA in the liver the amount of repeated sequences in this DNA fraction is increased (approximately by 10-11%), whereas the type of renaturation of a transcriptionally inactive major DNA fraction (DNA-II), making up to approximately 70% of total DNA, remains unchanged. The renaturation kinetics of a weakly extractable DNA fraction (DNA-III) making up to 5-10% of total DNA are similar to those of the major DNA fraction. Under cortisol-induced transcription the number of repeated sequences in this fraction is decreased as compared to DNA-III of intact liver (by approximately 10-12%). The increase of the number of repeated sequences observed after 4-8 hrs (i. e. peak of induction) is decreased after 16 hrs, resulting in a complete reconstitution of the original type of DNA-I renaturation on the 24th post-induction hour.