Incorporation of 5-iodo-2′-deoxyuridine (IUdR) into SV40 DNA

Abstract

The effect of various amounts of 5-iodo-2′-deoxyuridine (IUdR) on Simian Virus 40 (SV40) infected African green monkey kidney (AGMK) cells was investigated in respect to: (1) degree of IUdR incorporation into viral DNA, (2) yield of viral DNA, (3) viral coat protein synthesis, (4) infectivity of IUdR-substituted SV40 DNA. Rather than the absolute concentration it is the ratio of IUdR to thymidine (TdR) in the culture medium which determines the effect of the drug. The degree of IUdR incorporation into viral DNA was linearly dependent upon the relative amount of IUdR in the TdR plus IUdR precursor mixture added to the culture medium. The amount of viral DNA synthesized decreased exponentially with increasing degrees of IUdR substitution. Coat protein formation as determined by immunofluorescence microscopy behaved similar. At equal concentrations of IUdR and TdR, when considerable amounts of viral DNA and capsid proteins were still formed, complete virions were assembled. The infectivity of the IUdR substituted viral DNA was greatly reduced. Illumination studies of the IUdR containing SV40 DNA showed that “visible” light induced single strand breaks into this DNA at neutral pH. The lack of production of infectious SV40 virus in cultures treated with IUdR can be attributed to two major effects: (1) suppression of viral DNA synthesis, (2) reduced infectivity of the IUdR-substituted viral DNA that is produced.