Metal ion catalysis during the exon-ligation step of nuclear pre-mRNA splicing: Extending the parallels between the spliceosome and group II introns
- 1 February 2000
- journal article
- research article
- Published by Cold Spring Harbor Laboratory in RNA
- Vol. 6 (2), 199-205
- https://doi.org/10.1017/s1355838200992069
Abstract
Mechanistic analyses of nuclear pre-mRNA splicing by the spliceosome and group II intron self-splicing provide insight into both the catalytic strategies of splicing and the evolutionary relationships between the different splicing systems. We previously showed that 3′-sulfur substitution at the 3′ splice site of a nuclear pre-mRNA has no effect on splicing. We now report that 3′-sulfur substitution at the 3′ splice site of a nuclear pre-mRNA causes a switch in metal specificity when the second step of splicing is monitored using a bimolecular exon-ligation assay. This suggests that the spliceosome uses a catalytic metal ion to stabilize the 3′-oxyanion leaving group during the second step of splicing, as shown previously for the first step. The lack of a metal-specificity switch under cis splicing conditions indicates that a rate-limiting conformational change between the two steps of splicing may mask the subsequent chemical step and the metal-specificity switch. As the group II intron, a true ribozyme, uses identical catalytic strategies for splicing, our results strengthen the argument that the spliceosome is an RNA catalyst that shares a common molecular ancestor with group II introns.Keywords
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