INCREASE OF DNA POLYMERASE ACTIVITY FIRMLY BOUND TO NUCLEI DURING THE DNA SYNTHETIC PHASE OF THE CELL CYCLE
1973; Wiley; Volume: 6; Issue: 3 Linguagem: Inglês
10.1111/j.1365-2184.1973.tb01619.x
ISSN1365-2184
AutoresN.Burr Furlong, William Briscoe Novak, T. E. Stubblefield,
Tópico(s)Carcinogens and Genotoxicity Assessment
ResumoABSTRACT DNA polymerase activities were measured on nuclear and supernatant fractions obtained from hamster fibroblast cells (the Don‐C clone) grown in tissue culture and mitotically synchronized by selective removal of cells arrested in metaphase following a brief exposure to colcemid. A reproducible fraction (5–10%) of the polymerase activity was found to remain bound in the nuclear pellet after repeated cycles of freezing and thawing. The specific activity of this firmly‐bound nuclear DNA polymerase was found to increase during S‐phase in proportion to DNA synthesis. The bulk of this activity, after extraction in 1 m salt, exhibited an S value of 8·7 on neutral high salt sucrose gradients and was 24 times more active with poly dA. dT 10 as template than with heat denatured DNA. The rest of the cellular DNA polymerase activity showed no significant variation correlated with the cell cycle. This activity also had an S value from 8 to 9 but it was only 2·8 times more active with the homopolymer template than with heat denatured DNA. DNA polymerase activity similar to the firmly‐bound activity was found in extracts prepared from metaphase chromosomes.
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