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Molecular and Cellular Biology, August 2006, p. 6016-6023, Vol. 26, No. 16
0270-7306/06/$08.00+0 doi:10.1128/MCB.02347-05
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
J. David Barrass,
Alastair P. Droop,
Christophe Dez, and
Jean D. Beggs*
Wellcome Trust Centre for Cell Biology, University of Edinburgh, King's Buildings, Mayfield Road, Edinburgh EH9 3JR, United Kingdom
Received 8 December 2005/ Returned for modification 30 January 2006/ Accepted 30 May 2006
The Ntr1 and Ntr2 proteins of Saccharomyces cerevisiae have been reported to interact with proteins involved in pre-mRNA splicing, but their roles in the splicing process are unknown. We show here that they associate with a postsplicing complex containing the excised intron and the spliceosomal U2, U5, and U6 snRNAs, supporting a link with a late stage in the pre-mRNA splicing process. Extract from cells that had been metabolically depleted of Ntr1 has low splicing activity and accumulates the excised intron. Also, the level of U4/U6 di-snRNP is increased but those of the free U5 and U6 snRNPs are decreased in Ntr1-depleted extract, and increased levels of U2 and decreased levels of U4 are found associated with the U5 snRNP protein Prp8. These results suggest a requirement for Ntr1 for turnover of the excised intron complex and recycling of snRNPs. Ntr1 interacts directly or indirectly with the intron release factor Prp43 and is required for its association with the excised intron. We propose that Ntr1 promotes release of excised introns from splicing complexes by acting as a spliceosome receptor or RNA-targeting factor for Prp43, possibly assisted by the Ntr2 protein.
Permanent address: W. M. Keck Science Center of the Claremont Colleges, Claremont, CA 91711.
Present address: Department of Biology (Area 7), University of York, York YO10 5YW, United Kingdom.
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