FIG. 4.

(A) Schematic representation of subgenomic HPV-16 expression plasmids pBELM, pT2, and pT3. 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 these plasmids are indicated below. The L1 probe used for Northern blotting is indicated. Mut, a mutant L1 gene in which splicing silencers have been inactivated (11, 61). (B) Northern blot of cytoplasmic RNA extracted from HeLa cells transfected with pBELM, pT2, or pT3 in the absence or presence of a PTB-expressing plasmid. The blot was probed with the L1 probe. Gels were also probed for GAPDH expression. The position of the L1 mRNA is indicated. +, present; −, absent.