FIG 3.

Time-of-addition assay defines reverse transcription to be the antiretroviral target of ribonucleoside analogs. Permissive target cells were synchronously infected with the HIV-1 vector (time zero). At sequential time intervals postinfection, each ribonucleoside analog was added at the EC₇₅ and EC₉₀ to monitor the increase in viral infectivity, which is indicative of a phase during viral replication that is no longer susceptible to inhibition. The nucleoside reverse transcriptase inhibitor 3TC, which is a chain terminator of reverse transcription, was used as a control (it blocked replication at ∼2.5 h postinfection). HIV-1 vector replication was blocked at ∼3.5 h for 3-deazauridine and between 2 and 4 h for 2′-C-methylcytidine, 8-azaadenosine, and formycin A. The data shown are representative of those from three independent experiments.