Journal
GENES & DEVELOPMENT
Volume 21, Issue 7, Pages 811-820Publisher
COLD SPRING HARBOR LAB PRESS, PUBLICATIONS DEPT
DOI: 10.1101/gad.1524307
Keywords
intron; RNA dynamics; helicase; DExD-box protein; Prp5p
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Funding
- NIGMS NIH HHS [R01 GM040478, GM 040478] Funding Source: Medline
- NATIONAL INSTITUTE OF GENERAL MEDICAL SCIENCES [R01GM040478] Funding Source: NIH RePORTER
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Nuclear pre-messenger RNA (pre-mRNA) splicing requires multiple spliceosomal small nuclear RNA ( snRNA) and pre-mRNA rearrangements. Here we reveal a new snRNA conformational switch in which successive roles for two competing U2 helices, stem IIa and stem IIc, promote distinct splicing steps. When stem IIa is stabilized by loss of stem IIc, rapid ATP-independent and Cus2p-insensitive prespliceosome formation occurs. In contrast, hyperstabilized stem IIc improves the first splicing step on aberrant branchpoint pre-mRNAs and rescues temperature-sensitive U6-U57C, a U6 mutation that also suppresses first-step splicing defects of branchpoint mutations. A second, later role for stem IIa is revealed by its suppression of a cold-sensitive allele of the second-step splicing factor PRP16. Our data expose a spliceosomal progression cycle of U2 stem IIa formation, disruption by stem IIc, and then reformation of stem IIa before the second catalytic step. We propose that the competing stem IIa and stem IIc helices are key spliceosomal RNA elements that optimize juxtaposition of the proper reactive sites during splicing.
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