Age changes in the H1 group of histones from rat liver

Histones were obtained from young and old rat livers by extracting them in 0.25 N HCl. They were fractionated on 15% acid urea polyacrylamide gels containing 6.25 M urea and the changes in the ratio of the major histone fractions as a function of age were calculated. Data presented show a significant increase in the amount of H1 degree fraction in the liver of old rats as compared to young rats. This data is discussed and the possible involvement of H1 degree fraction in an increased resistance of old rat liver chromatin to micrococcal nuclease digestion of linker DNA is suggested. Finally, in connection with this increased resistance, some possible consequences in chromatin structure are discussed.