The template activity, nucleosomal pattern and thermodenaturation parameters of transcriptionally low active (TLA) and transcriptionally active liver chromatin fractions were studied in adult (6–8 months) and old (26–28 months) rats. The following age-related changes of chromatin template properties were found: decrease of endogenous DNA polymerase α- and β-activity in vitro in both chromatin fractions, and redistribution of newly synthetized RNA between mono- and oligonucleosomes in the TLA fraction. These changes are thought to be connected with age-related reorganization of chromatin structure, i.e. with increase of DNA-protein interactions, which stabilize association of chromatin supranucleosomal structures.

No abstract

Replicating spleen and kidney DNA of 6-month (adult) and 24-month (old) rats labeled with ³H-thymidine was separated to single-stranded and double-stranded fractions by hydroxyapatite chromatography. The relative quantity of single-stranded DNA was decreased during labeling. This decrease, accompanied by increase of specific radioactivity of double-stranded DNA or formation rate of double-stranded DNA, was smaller in old spleen and kidney as compared with adult ones. The above age-dependent decrease was more pronounced in tissue with higher mitotic activity (spleen). Decreased DNA replication rate may cause age-dependent disturbances of cell renewal.

No abstract

The rate of growth of the DNA chain length was found to decrease in rat spleen with aging. This can be substantiated by the slowing down of transformation of old spleen ³H-labeled DNA with low molecular weight to that with high molecular weight as labeling time increases. At the same time, the intensity of the DNA total synthesis is higher in old spleens than in adult ones. This may result from an increase of mitotic activity in rodent spleen with aging. In its turn, the increased mitotic activity may represent an adaptive reaction responsible for maintaining the number of immunocompetent cells which tend to decrease with aging. The slowing down of the newly formed DNA chain growth may lead to the decreased rate of stabilization of the secondary structure of replicating DNA in old spleen.