title: Variation of two forms of DNA polymerase-alpha during a HeLa cell cycle.
abstract: HeLa cells contain two forms of DNA polymerase-alpha (P-I and P-II) with varied affinity to DNA, separable on a DNA-cellulose column. The activity of each form was followed during a cell cycle of synchronized culture of the HeLa cells. P-I was recovered from the nuclear extract and P-II from the cytoplasmic fraction. The P-I activity remained at a low level during M to G1 phase until a marked increase between late G1 and S phases, while P-II activity increased gradually throughout the period. Both activities attained their highest level at mid-S phase and then the P-I activity declined more rapidly than the P-II. Addition of hydroxyurea at mid-S phase inhibited the decrease of both enzyme activities. The enzyme activity of nuclear extract from S phase cells was not inhibited by mixing with extract from M phase cells. When the cytoplasmic fraction from M phase cells was chromatographed on a DNA-cellulose column, single activity peak was observed at the position of P-II. These results suggest that the decrease in P-I activity is neither due to the presence of an inhibitor nor to mere release of the enzyme from chromosomes.
mesh_terms: D002453:Cell Cycle; D004256:DNA Polymerase I / Q000032:analysis*; D004257:DNA Polymerase II / Q000032:analysis*; D004273:DNA, Neoplasm / Q000096:biosynthesis; D004259:DNA-Directed DNA Polymerase / Q000032:analysis*; D006367:HeLa Cells / Q000166:cytology / Q000201:enzymology; D006801:Humans; D007399:Interphase; D008677:Metaphase
chemical_list: D004273:DNA, Neoplasm; D004256:DNA Polymerase I; D004257:DNA Polymerase II; D004259:DNA-Directed DNA Polymerase