Low molecular weight DNA polymerase: decreased activity in spleens of old Balb/c mice

The DNA polymerase activities in the spleens of young adult (3-8 months) and senescent (24-30 months) female BALB/c mice have been examined. Comparisons were made by direct assay of activated DNA-dependent and (rA)n-(dT)n-dependent activities in extracts from cytoplasmic and neclear fractions and also by sucrose gradient sedimentation analysis of the two major forms of DNA polymerase activity was equivalent in the spleens of young and old BALB/c mice. The low molecular weight DNA polymerase activity was decreased in the spleens of old BALB/c mice. This decreased activity was reflected most markedly in the nuclear fraction of the spleens. Mixing experiments did not indicate the presence of inhibitors in the nuclear extract from the old mouse spleens. Stepwise extractions of isolated nuclei with increasing NaCl concentrations showed consistent results without revealing any difference in extractability of the low molecular weight DNA polymerase from the old mouse chromatin. Isolated low molecular weight DNA polymerase preparations from the young and old BALB/c mouse spleens are similar in chromatographic migration, sucrose gradient sedimentation, heat lability in vitro and Km of substrates. The low molecular weight DNA polymerase activity was not found to decline in livers and kidneys of 24 to 30-month-old BALB/c mice, nor in spleens of 30 to 34-month-old BC3F1 mice.