Role of deoxyribonucleic acid polymerase beta in nuclear deoxyribonucleic acid synthesis.

Exonuclease activity has been measured in preparations of both enzymes. The activity associated with DNA polymerase a requires denatured DNA, Mg2+ and is ATP-dependent. The polymerase b-associated nuclease requires denatured DNA and Mg2+ or Caz+. Studies of the distribution of these enzymes during the cell cycle have shown that extracts of cells harvested at the time of nuclear DNA synthesis (Chiang & Sueoka, 1967) have DNA polymerase b as the predominant DNA-synthesizing activity, whereas DNA polymerase a is the major activity in cells harvested at a resting phase of growth. The two major DNA polymerases of Chlamydomonas reinhardii therefore seem to differ in physical and enzyme properties and in the time of appearance during the vegetative cell cycle.