In vitro analysis of mutants from the U5-IR loop library. Panel A: Initiation of reverse transcription. Panels B: End processing by RSV integrase. Experiments were carried out as described in the legend to Figure 4. In all panels, the sample numbers refer to clones listed in Table 2. Two additional substrates derived from clone IRL-10 were examined, which substitute the wild type base pair at position 89 and 93, respectively.