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Free keywords:
Catalytic centre; Cwc2; RBM22; spliceosome; U6-ISL
Abstract:
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.
