The Demonstration of Separate DNA Polymerase Activities In Intact Isolated Rat Liver Nuclei by Means of Response to Bleomycin and Arabinosyl Cytosine 5-Triphosphate

Abstract

In nuclei from normal rat liver, all DNA synthesis measured as 3H-TTP incorporation occurs during the 1st 20 min of incubation. This incorporation is partially inhibited by the antitumor agent ara-CTP [arabinosyl CTP]. The portion that is inhibited by ara-CTP represents de novo DNA synthesis in progress in the liver nuclei at the time of isolation. The insensitive portion probably represents unscheduled DNA polymerase activity, and may be a repair response to preparation. Bleomycin produces increased 3H-TTP incorporation, which is sustained over the entire hour of incubation. Addition of ara-CTP and bleomycin produces a sustained increase that is slightly smaller at all points except at 1 h. The data are consistent with the hypothesis that single strand DNA breaks produced by bleomycin can also result in the initiation of this activity, and this activity is distinguished from the activity that rises following partial hepatectomy (putative replicase) by its lack of inhibition by ara-CTP. Similar results were reported in 2 other types of animal cell nuclei in which phleomycin stimulated 3H-TTP incorporation into DNA.