HISTONE VARIANTS, H(1) SUBTYPES AND OTHER CHROMATIN PROTEINS AS BIOMARKERS OF AGE AND CALORIC RESTRICTION IN RATS

The synthesis and phosphorylation levels of basic chromatin proteins f rom cell cycle phases of dividing bone marrow cells in Fischer 344 rat s were investigated by gel electrophoresis. Two groups of rats, young ad libitum (Y/A 3 mo.) and old ad libitum (O/AL 28 mo.), had free acce ss to rat chow, and a third group of old rats was maintained on a calo rie-restricted intake (O/CR 28 mo.). Histone H-1 subtypes a, b and c f rom combined S+G2 phase revealed highest amounts of [H-3] lysine incor poration in Y/AL, lowest in O/AL, and intermediate levels in O/CR anim als, while subtypes e and I-degrees were highest in O/AL, lowest in Y/ AL, and mid level in O/CR. The P-32-orthophosphate incorporation of th ese subtypes followed a parallel scenario as with lysine. Histone H-4 variants from S phase demonstrated the highest levels of lysine labeli ng in O/AL, lowest in Y/AL and intermediate levels in O/CR. The H-1 va riants were similar in synthesis patterns to H-4 variants but less dra matic. Minor histone variants M2, M3 and M4 manifested most synthesis in O/AL, least in Y/AL and mid levels in O/CR. Conversely, M1 synthesi s was high in Y/AL, low in O/AL and modest in O/CR. Ubiquitin followed a similar pattern in lysine labeling to M1 and A24 which was inversel y proportional to ubiquitin. The metabolic activity of these basic pro teins in O/CR exemplifies a condition characteristic of Y/AL animals m odulated by age and diet dependent factors.