In vitro suppression of the 3′SS mutation by selected prp8 alleles. Wild-type (lanes 1,4), U+2A (lanes 2,5), and UAG → UUG (lanes 3,6–16) pre-mRNAs were incubated in extracts prepared from wild-type PRP8 (lanes 1–3,15,16) or selected prp8 allele (lanes 4–14, as indicated) strains. Positions of pre-mRNA, lariat intermediate, and lariat products are indicated.