Alterations in chromatin functions during aging in vitro.

Age-associated alterations in the chromatin functions of human diploid cells have been observed. These alterations include: (1) a decline in the rate of histone acetylation; (2) a reduction in the rate of RNA synthesis as measured by (a) the rate of 3H-uridine incorporated into the RNA of young and old cells; (b) comparison of the template activity of isolated chromatin from young and old cells using E. coli RNA polymerase and (c) measurement of chromatin template activity using the endogenous RNA polymerase of young and old cells. It is suggested that the nondividing state of old cells may be the result of the inability to synthesize specific RNA molecules (and perhaps specific proteins) necessary for the cell to continue through the cell cycle.