[Structural-functional characteristics of chromatin fractions in the regenerating liver of adult and old rats].

The transcriptional activity, nucleosomal patterns, and thermodenaturation parameters of low-active and active fractions of liver chromatin were studied in adult (6-8 mo) and old (26-28 mo) rats at 2, 4, and 6 weeks after partial hepatectomy. At 2 weeks postoperatively, there was a decrease in relative specific radioactivity (RSR) of the active chromatin fraction in adult rats, which returned to normal by the 4th week, while in the low-active fraction it was decreased throughout all the studied regeneration periods. The decrease of the low-active fraction RSR was attended with changes in the nucleosomal organization and DNA-protein interactions revealed by electrophoresis and thermodenaturation. Old rats were found to have the active fraction RSR unchanged throughout all the studied regeneration periods. The low-active fraction RSR increased at 2 and 4 postoperative weeks and decreased to the level of intact liver at 6 weeks. Electrophoretic analysis and parameters of thermodenaturation of the low-active fraction reflect changes in the chromatin conformation associated with transcription activation and, at the same time, reveal its higher compactness in nucleosomal structures. Age differences in the time-course of structural rearrangements and transcriptional activity of liver chromatin during regeneration may be responsible for different rates of postoperative liver restoration in adult and old rats.