The mechanism of action of 9-(1,3-dihydroxypropoxymethyl)guanine (DHPG) and phosphonoformic acid (PFA) but not 5-fluorouridinedeoxyribose (FUdR), provides selective action against cytomegalovirus (CMV)-coded events and this was used to demonstrate that the synthesis of viral DNA was continuous during the extended phase of virus growth. The synthesis of viral DNA was measured by restriction enzyme analysis after exposure to [P]orthophosphate and its interruption by DHPG or PFA resulted in a cessation in the extrusion of infective virus from treated cells. The rate of decline in infectivity appeared to correspond to the failure of cells to maintain the synthesis of late proteins once DNA synthesis was blocked. Thus, regulation of late protein synthesis appeared to be linked to synthesis of viral DNA even at late stages in CMV growth. The synthesis of the polyamines spermidine and spermine, considered obligatory for CMV growth, was unaffected by early or late inhibition of viral DNA and this showed that some virus-induced events were unaffected by the restriction on virus growth by DHPG. This provided evidence that polyamine biosynthesis was a target independent of viral DNA synthesis , which may be important in future considerations of combined drug therapies.

Keyword(s): CMV , DHPG and polyamines

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