Cell cycle dependent activities of DNA polymerases alpha and delta in Chinese hamster ovary cells

The activities of DNA polymerases alpha and delta, in extracts from Chinese hamster ovary (CHO) cells, were assayed in order to determine whether these polymerases are regulated during the cell cycle. An exponential population of CHO cells was separated into enriched populations of G-1, S, and G-2/M phases of cell cycle by centrifugal elutriation. Total cell homogenates from each population were assayed for DNA polymerase activity by measuring labeled nucleotide incorporation into the exogenous templates oligo(dT).poly(dA) and DNase I activated calf thymus DNA. In these experiments, specific DNA polymerase inhibitors were added to assays of the cellular extracts to allow for the independent measurement of activities of DNA polymerases alpha and delta. Comparisons of total DNA polymerase activity from cellular extracts, sampled from each portion of the cell cycle, demonstrated no significant change with respect to the concentration of total protein. However, results indicate that the activity of DNA polymerase delta increases with respect to that of DNA polymerase alpha in the G-2/M portion of the cell cycle. This difference in relative activities of DNA polymerases alpha and delta suggests a coordinate regulation of a specific species of DNA polymerase during the cell cycle.