An accessory protein of DNA polymerase alpha declines in function with increasing age.

Isoforms of DNA polymerase alpha (pol alpha/primase; pol alpha) were isolated from the livers of C57BL/6 mice either 3 months old (young) or 13 months old (mature). The 13-month-old mice were from two groups, one in which food was available ad libitum (AL), and one in which calories had been restricted to 60% of the AL intake (CR). The polymerases from young vs. mature and CR vs. AL mice differed in total and specific pol alpha activity, with the highest values exhibited by enzymes from 3-month-old mice. A more active isoform of pol alpha was typically isolated from CR animals than from AL animals. Differences in charge were used to chromatographically separate pol alpha into elution peaks exhibiting differing degrees of enzyme activity. DNA pol alpha isolated from tissues of mature mice exhibited a decline in activity which was not associated with decreased recoverable levels of pol alpha protein, but with a decline in the tendency of pol alpha to co-purify with an accessory protein, alpha AP, that binds double-stranded DNA (dsDNA). Low activity pol alpha isoforms which did not co-purify with alpha AP were stimulated by interaction with exogenous alpha AP. Pol alpha isoforms which co-purified with the dsDNA-binding accessory protein exhibited higher specific activity and less enhancement of activity upon interaction with exogenous alpha AP. Calorie restricted animals exhibited a pol alpha isoform that was more like pol alpha from younger animals in that it typically copurified with alpha AP, the DNA-binding accessory protein.