FIG 1.
HIV reverse transcription. Upon infection, the viral positive-strand RNA genome is copied into double-stranded DNA (dsDNA) by the viral reverse transcriptase. The cellular tRNALys3 binding to the primer binding site (PBS) functions as a primer for minus-strand DNA synthesis (step 1). After being reverse transcribed, the viral RNA template is degraded by the RNase H activity of reverse transcriptase, but the 3′PPT (indicated with PPT) and central PPT (cPPT) motifs resist cleavage and function as a primer for plus-strand DNA synthesis (steps 4 and 5). Complementarity of the sequences at the termini of the partially double-stranded linear HIV DNA induces circularization to form 1-LTR circles (step 7). Subsequent continuation of second-strand DNA synthesis and linearization, which involves strand displacement of the LTR sequences, results in a linear dsDNA molecule with complete LTR motifs at both termini (steps 8 and 9). This full-length 2-LTR dsDNA is integrated into the cellular DNA by the viral integrase protein (step 10a; no DTG). When integration is blocked, for example in the presence of DTG, 2-LTR circles accumulate (step 10b). The red star indicates the 3′ end of the 3′PPT RNA fragment, and the yellow star indicates the 5′ end of the 5’LTR in the 2-LTR dsDNA products.