CHANGES IN THE DISTRIBUTION OF POLYMERASE ACTIVITY DURING DNA SYNTHESIS IN MOUSE FIBROBLASTS

Abstract

When suspension cultures of mouse fibroblasts were partially synchronized with 5-fluorodeoxyuridine, DNA synthesis was most active three hr after release of the 5-fluorodeoxyuridine block with thymidine. DNA polymerase activity in the supernatant fraction of the cell decreased 21 per cent from just before thymi-dine release to three hr after release. During the same period, polymerase activity in the particulate fraction increased 21 per cent, although the absolute amount of increase accounted for only 9 per cent of the decrease in supernatant activity. These results suggest that at the time of DNA synthesis supernatant polymerase became particulate and less active in terms of the usual assay conditions.