Age-Related Alterations in the Structure of DNA

Abstract

DNA prepared from livers of aging rats (above 2 yr. of age), with 1-2% histone content, behaved on thermal denaturation like DNA from livers of young animals with about 6% histone content, showing increased Tm-values and increased loss of hyperchromism on cooling after denaturation. This stabilizing effect in old DNA was visible only at ionic strengths below 0.01. At higher ionic strengths (up to 0.9) Tm shows a linear dependence on log ionic strength independent of age of the animal or histone content The apparent reversibility of denaturation by up to 80% at high ionic strength, shown by the loss of thermal hyperchromism, was shown not to consist of double-helix reformation, but probably of single-helix formation, with base-stacking bonds responsible for the loss of hyperchromism. These results were in accord with the recently proposed model of cellular aging, based on the concept of progressive irreversible blocking of genes by protein repressor.