Premature reverse transcription can be blocked. HIV-1 was expressed from 293T cells transfected either in the absence (black bars) or presence (red bars) of RTIs. Virus was harvested and treated with DNase I and subtilisin, as described in the Methods section (Figure 1, right). Quantities of intravirion DNA were then measured by qPCR using the reverse transcription intermediate targets  indicated at the bottom of the figure (tRNA, red line; minus-strand DNA, black line; plus-strand DNA, blue line; target sequences indicated by the black dumbbells). The quantities expressed are the ratio of vDNA to gRNA. Panel A shows wild-type virus, panel B shows NCH23C virus, and panel C shows NCH44C virus. Values plotted are the means and the errors bars are the standard deviations from two separate experiments.