AGE-RELATED-CHANGES IN EXPRESSION AND ACTIVITY OF DNA-POLYMERASE ALPHA - SOME EFFECTS OF DIETARY RESTRICTION

DNA polymerase (alpha (pol alpha) purified from human diploid fibrobla sts (HDF) and from livers of C57BL/6N mice showed age-related decrease s in: (1) mRNA levels; (2) the amount of enzyme isolated per cell; and (3) enzyme activity (HDF); as well as: a) the amount of enzyme isolat ed; b) the specific activity; and c) the enzyme fidelity (liver). Hepa tic pol alpha from dietary restricted (DR) mice exhibited less of a de cline in specific activity and copied synthetic DNA templates with rel atively higher fidelity than did enzymes from animals fed ad libitum ( AL). Pol alpha from fetal-derived HDF exhibited increased expression c ompared with aged donor-derived HDF, with both fetal and old cell pol alpha in normal cells being expressed at lower levels than in their tr ansformed cell corollaries. Treatment of human pol alpha from aged don or-derived HDF with a pol alpha accessory protein isolated from log ph ase murine cells resulted in increased pol alpha binding of DNA and in creased pol alpha activity. However, highly active pol alpha isolated from fetal-derived or transformed HDF, or from transformed murine cell s, showed little or no activity enhancement in the presence of accesso ry protein. These data indicate that, as a function of increased age, there is a decrease in pol alpha expression and specific activity in H DF, as well as decreases in specific activity and fidelity of pol alph a in essentially amitotic murine hepatic tissues. Dietary restriction impedes the age-related declines in both activity and fidelity of hepa tic pol alpha in mice. The data further indicate that transformation o f slowly dividing HDF is associated with increased expression of pol a lpha, but suggest that increased expression alone is not sufficient to explain the difference in polymerase activity levels between parental and transformed HDF. Lastly, the data suggest that interaction of pol alpha with an essential accessory protein may be altered as a functio n of age, an alteration that appears to be correlated with the decline in pol alpha DNA binding and specific activity.