Ageing studies in rat liver. I. Complexity of RNA from two to ten months of age.

A highly sensitive nucleic acid hybridization assay was used to compare the extent of nonrepetitive DNA transcription in rat liver between the ages of two and ten months. The basic approach consisted on initially purifying the DNA expressed in liver at these ages and then using it in reactions with homologous and heterologous RNAs. Such experiments failed to reveal any differences in nonrepetitive DNA transcription as a function of age. The possibility was also explored that there might be an age-associated variation in the proportion of the total RNA complexity attributable to poly(A+) RNA. These experiments, too, were negative in that the poly(A+) RNA was found in all cases to account for approximately 50% of the total sequence diversity. Overall, these data strongly suggest that ageing is not accompanied by a steady, progressive change in the regions of the genome transcribed, either quantitatively or qualitatively.