Characterization of Cwc2, U6 snRNA, and Prp8 interactions destabilized by Prp16 ATPase at the transition between the first and second steps of splicing

U6 alleles upstream of ACAGA motif support transition from the first-to-second steps of splicing. (A) Prp16 promotes transition from the first to the second step, whereas prp16-302 allele inhibits this transition. (B) Schematic representation of U6 (red), U2 (green), and pre-mRNA (gray) at the catalytic center of the spliceosome. Mutations of U6 in the ₄₁AACAAU₄₆ region are marked. In prp16Δ U6Δ strain (yCQ166), prp16-302 (C) and prp16-R686I (D) alleles inhibit transition to the second step, exhibiting cs phenotypes suppressed by mutations within the U6 region ₄₁AACAAU₄₆, as shown by spotting on 5FOA plates. (E) Growth curves (OD₆₀₀) of yeast strains harboring prp16-302 allele in combination with U6-A42g and A44c alleles exhibit improved growth, compared to U6-WT at 16°C.