Induction and regulation of DNA nucleotidyltransferase activity in fish cells infected with frog virus 3

Abstract

Infection of fathead minnow (FHM) cells with frog virus 3 (FV 3) at 28° induced synthesis of deoxyribonucleic acid (DNA) polymerase and viral DNA in the cell cytoplasm starting between 1 and 2 hours after infection. By 4 hours, increase in DNA polymerase synthesis terminated and enzyme activity in infected cells was 4–15 times greater than in uninfected cells. Viral DNA synthesis was completed by 10–12 hours which corresponded to a single cycle of virus growth. Induction and “swith-off” of enzyme synthesis were not affected by treatment of the infected cells with 1-β- d-arabinofuranosylcytosine, an inhibitor of DNA synthesis and FV 3 growth. Increase of DNA polymerase activity ceased immediately after addition of cycloheximide or actinomycin D during enzyme synthesis, suggesting that enzyme formation required de novo protein synthesis and continuing messenger ribonucleic acid synthesis. It is concluded that synthesis of DNA polymerase is an “early” function of the parental viral genome. Replication of viral DNA is not required to initiate or “switch-off” formation of this early enzyme.