FIG. 1.

PCBP-RNA interactions within stem-loop IV of the poliovirus IRES. (A) Footprinting analysis reveals that PCBP protects several regions of the large stem-loop IV from RNase digestion. The viral 5′UTR was treated with RNase T₁ (lanes 5 to 8) or RNase T₂ (lanes 9 to 12). Lane 13 corresponds to untreated RNA. RNase was added in the presence of bovine serum albumin (−) or PCBP protein, as indicated at the top of each lane. Primer extension was performed by using a primer complementary to nucleotides 368 to 408. Lanes labeled C, T, A, and G correspond to dideoxy sequencing lanes. Brackets indicate PCBP protected regions (a, b, and c). The numbers on the left indicate the nucleotide position of the viral genome in poliovirus type 1. (B) Predicted secondary structure of stem-loop IV of the poliovirus type 1 genome. PCBP protected regions as determined by footprinting analysis in panel A are indicated by black lines (loop a, loop b, and bulge c).