1. The synthesis of RNA in purified nuclei of tissues from aged mice is substantially diminished. 2. As judged by the recovery of RNA in 105000g supernatants of tissue homogenates, the synthesis of ribosomal RNA may be particularly affected. 3. The decrease in RNA synthesis may be due to changes in the composition of the nuclear-associated protein with age, which result in changes in the priming ability of tissue chromatin. 4. Aging is accompanied by marked changes in the sedimentation profiles of ribonucleoprotein particles. These can be attributed to an age-associated depletion in messenger RNA or to an increased susceptibility to enzymic disaggregation.
