A transcriptional block to elongation abrogates TFIIS-dependent exon skipping. (A, upper panel) Presence of TFIIS enhances exon skipping in dyn2 U[−2]C. Strains JAY698 (ppr2Δ) and JAY699 (PPR2) were transformed with pU[−2]C and grown at 30°C. (A, lower panel) Analysis of signals, as described in previous figure legends (n = 3). E2+, E2−, or E2−/E2+ values were compared between TFIIS+ and TFIIS− strains; P values indicate the likelihood that the differences in these values are due to sampling error. (B) Schematic of the pGSlacIAt template with the lacI operator sequence (laco). Yeast strain CMKY21 (ppr2Δ) carrying plasmids pGSlacIAt and a methionine-repressible lacI expression construct were transformed with a high-copy (H) or low-copy (L) PPR2 expression construct or appropriate high-copy or low-copy empty vector (−). (C) Primer extension (upper panel) and graph of exon skipping ratios (lower panel; E2−/E2+ ±SEM, n = 3).
