FIG. 3.

(A) Schematic representation of subgenomic HPV-16 expression plasmids used to study the induction of late gene expression by PTB. Numbers indicate the nucleotide positions of 5′ splice sites (filled circles) and 3′ splice sites (empty circles) or the positions of pAE and pAL or mark the borders of deletions. Major potential mRNAs produced by pBEL and pBELM are indicated below the plasmids. Black bars represent the E4 and L1 probes used for Northern blotting. Mut, a mutant L1 gene in which splicing silencers have been inactivated (11, 61). (B, C, D, E, and F) Northern blots of cytoplasmic RNA extracted from HeLa cells transfected with pBEL, pBELM, pBELMDU, pBELMDPU, pBearly, p1-22 M, pBELDL2, pC16L1, or pC16L1M in the absence or presence of a PTB-expressing plasmid. Blots were probed with the E4 probe (D) or the L1 probe (B, C, E, F, and G). Gels were also probed for GAPDH or actin expression. Positions of the E4, L1, and L2/L1 mRNAs are indicated. +, present; −, absent.