Titer of NC mutant viruses is unchanged if premature reverse transcription is blocked. Results from HIV-1 produced either in the absence (black bars) or the presence (red bars) of RTIs are presented. All viruses produced were PEG precipitated, not just those treated with RTIs for direct comparison. Panel A shows the yields of viruses from transfections, with and without RTI treatment based on average exogenous-template RT activities (in counts per minute of [32P]-TMP incorporated per mL [CPM per mL]; error bars are the standard deviation from duplicate samples). Panels B and C are from two independent transfection-infection experiments and each displays the titers of viruses measured using TZM-bl cells, determined from 3-fold serial dilutions . The titer was corrected for dilution and input virus as determined by exogenous-template RT activity and expressed as "Normalized BCFU" from the means of at least 3 dilutions (error bars represent the standard deviation).