Datensatz

Zusammenfassung

RNA-structural elements play key roles in pre-mRNA splicing catalysis; yet, the formation of catalytically com- petent RNA structures requires the assistance of spliceo- somal proteins. We show that the S. cerevisiae Cwc2 protein functions prior to step 1 of splicing, and it is not required for the Prp2-mediated spliceosome remodelling that generates the catalytically active B* complex, suggest- ing that Cwc2 plays a more sophisticated role in the generation of a functional catalytic centre. In active spli- ceosomes, Cwc2 contacts catalytically important RNA ele- ments, including the U6 internal stem-loop (ISL), and regions of U6 and the pre-mRNA intron near the 5 0 splice site, placing Cwc2 at/near the spliceosome’s catalytic centre. These interactions are evolutionarily conserved, as shown by studies with Cwc2’s human counterpart RBM22, indicating that Cwc2/RBM22–RNA contacts are functionally important. We propose that Cwc2 induces an active conformation of the spliceosome’s catalytic RNA elements. Thus, the function of RNA–RNA tertiary inter- actions within group II introns, namely to induce an active conformation of domain V, may be fulfilled by proteins that contact the functionally analogous U6-ISL, within the spliceosome.