Variation of deoxyribonucleic acid polymerase activities during rat liver regeneration.

The existence of multiple molecular weight forms of DNA polymerase in different cellular locations of eukaryotie cells, and the demonstration that these enzyme activities have quite different properties (l-4) raise a number of questions about DNA metabolism in complex organisms. Some of these questions were implicit in the early work on mammalian DNA polymerase; particularly the demonstration that the DNA polymerase activity increase in regenerating rat liver was in the cytoplasmic fraction (5, 6). In this communication we re-examine the DNA polymerase activities in nuclear and cytoplasmic fractions from sucrose homogenates of regenerating rat liver and assay the level of the 3.4 and 6 to 8 S forms of polymerase in each of these fractions on sucrose gradients (1, 2). The results are quite conclusive in showing that the cytoplasmic 6 to 8 S enzyme is the activity that responds to the stimulus to proliferate.