A study of the mechanisms of DNA And thymine degradation in cultured human cells infected with a lipovirus.

DNA and thymine degradation on cultured human, mouse, and chick cells were studied. Significant increase in DNA-degrading activity was demonstrated in human embryonic cells killed by freeze-thawing, liver cells killed with mitomycin C, mouse embryonic cells infected with encephalomyocarditis virus, and in all cells killed by the lipovirus. Twelve other viral agents, actinomycin D, and 5-fluorodeoxyuridine failed to produce a similar increase. Thymidine-2-C(14)-labeled cultures, either live, killed, or infected by 19 different physical-chemical and biological agents, did not release detectable quantity of C(14)C(2). Following infection with the lipovirus 20 to 60 per cent of the total radioactivity of thymidine-2-C(14)-labeled cultures was liberated as C(14)O(2). It was postulated that the lipovirus introduced into the host cells the missing genetic information necessary for the synthesis of one or more enzymes responsible for the reductive catabolism of thymine.