Total RNA was prepared from MCHs and 293Ts stably transduced with HIV-CIB or HIV-LIB, respectively, and subjected to RT-PCR, using oligo(dT) as first strand primer. At top is shown a schematic of the region of the HIV vector amplified, with the DNA primers (arrows) located within the tat/rev (t/r) exons (rectangles). Truncated intron is ∼900 bp. RRE denotes Rev-response element. Bottom two panels: results using HIV primers using 3 different amounts of first strand reaction equivalent to RNA amounts of 15, 45, and 135 ng (wedges), Southern blotted using a 0.7 kb intronic probe (two different film exposure times; expected product of ∼1250 bp indicated by arrow). Top panel: Results using the same primers and amounts of first strand cDNA, with expected spliced product of 350 bp indicated by arrowhead (EtBr stain). Unspliced products have been cropped. No products were observed with water (H) control or in the absence of RT. These RT-PCR experiments were repeated twice with similar results. R denotes revertant cell line.