FIGURE 7.

Schematic of the interplay between Prp16 and Cwc25 in the first catalytic step. After Prp2-mediated dissociation of SF3a/b, Yju2 and Cwc25 bind to the spliceosome to promote the first catalytic reaction. Prp16 binds to the spliceosome after the binding of Yju2 and Cwc25, and mediate their dissociation after the transesterification reaction if the reaction is fast, or before transesterification if the reaction is slow, as in the case of brC mutant. The D473A mutant of Prp16 can stabilize the association of Cwc25 with the spliceosome to promote the transesterification reaction.