VARIATION OF 2 FORMS OF DNA POLYMERASE-ALPHA DURING A HELA-CELL CYCLE

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  • 1 January 1979
    • journal article
    • research article
    • Vol. 70  (4) , 527-532
Abstract
HeLa cells contain 2 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 Gl phase until a marked increase between late Gl 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. The decrease in P-I activity apparently is neither due to the presence of an inhibitor nor to mere release of the enzyme from chromosomes.