Effect of treatment in vivo with N,N-dimethylnitrosamine or methyl methanesulphonate on the cytoplasmic DNA polymerase of regenerating rat liver.

A 10-16 fold increase in rat liver cytoplasmic DNA polymerase (DNA polymerase-alpha) was observed by 24 hrs after two thirds partial hepatectomy. Injection of either N,N-dimethylnitrosamine (DMN) or methyl methanesulphonate (MMS) At 6 or 12 hrs after partial hepatectomy completely inhibited this increased production of polymerase, but when given at 20 hours they had less effect. Neither compound altered the molecular size distribution of the enzyme. These data indicate that the lowered levels of DNA polymerase-alpha could play a major role in the reduction in DNA synthesis which occurs after carcinogen treatment.