Cytoplasmic synthesis of viral DNA early during infection and cell transformation by the murine sarcoma-leukemia virus.

Abstract

The intracellular site of virus-specific DNA synthesis was studied in mouse 3T6 cells early after efficient infection with the Harvey strain of murine sarcoma-leukemia virus. Treatment of cells with arabinosyl cytosine at different times after infection indicated that DNA synthesis at 1–4 h was essential for both the subsequent transcription of virus-specific RNA and the formation of progeny virus. Autoradiographic analysis of cells pulse-labeled with tritiated thymidine at different times after infection showed that DNA synthesis begins in the cytoplasm within 1 h after infection, reaches a maximal rate at 2 h, and decreases subsequently. Newly synthesized cytoplasmic DNA is rapidly transported to the nucleus, as indicated by autoradiographs of cells irradiated with ultraviolet light to block cell DNA synthesis, then infected with virus, pulse-labeled with tritiated thymidine and chased with unlabeled thymidine. The viral nature of newly synthesized cytoplasmic DNA was demonstrated by the isolation of labeled DNA from the cytoplasmic fraction at different times after infection that hybridized with viral 60–70S RNA.