Fluctuation in activity of the molecular forms of cellular DNA polymerase during infection by SV40.

Infection of BSC-1 cells by SV40 brings about an increase of 7--11-fold in DNA polymerase activity, found in the nuclei and cytoplasm, respectively. The overall ratio between activites of DNA polymerase beta (3.1S) and DNA polymerase alpha (5.5S) remains fairly constant throughout infection. However,there is a large increase in DNA polymerase alpha2 (7.1S) in the cytoplasm, and its appearance in the nuclei late in infection. The addition of 1 M NaCl to infected cytoplasm,causes an aggregation of DNA polymerase alpha into a higher sedimenting form (9.8S), termed DNA polymerase alpha3. DNA polymerase alpha1, alpha2 and alpha3 are different molecular forms of the same enzyme, as can be seen by their similar inhibition by N-ethyl-maleimide, heparin and NaCl. However, this new activity, alpha3, is stimulated by dithiothreitol to a greater extent at pH 9.30 than at pH 7.94. The conformational changes induced in DNA polymerase and its increase in activity during infection with SV40 are discussed.