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íkováDepartment of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814, USA
Interaction of the ends of the exons with loop 1 of the U5 snRNA aligns the exons for ligation in the second step of pre-mRNA splicing. To study the effect of Prp18 on the exons interactions, we analyzed the splicing of pre-mRNAs with random sequences in the exon bases at the splice junctions. The exon mutations had large effects on splicing in yeast with a Prp18 protein lacking its most conserved region, but not in wild-type yeast. Analysis of splicing kinetics demonstrated that only the second step was affected in vivo and in vitro, showing that Prp18and specifically its conserved regionplays a key role in stabilizing the interaction of the exons with the spliceosome at the time of exon joining. Superior exon sequences defined by the prp18 results accelerated the second step of splicing by wild-type spliceosomes with inefficient AT-AC pre-mRNAs, implying that normal exon interactions follow the rules we discerned for prp18 splicing. Our results show that As are preferred at the ends of both exons and support a revised model of the interactions of the exons with U5 in which the exons are arranged in a continuous double helix that facilitates the second reaction.
[Keywords: pre-mRNA splicing; U5 snRNA; Prp18; spliceosome]
Received February 5, 2007; revised version accepted March 19, 2007.
E-MAIL dhorowitz{at}usuhs.mil; FAX (301) 295-3512.
Supplemental material is available at http://www.genesdev.org.
Article is online at http://www.genesdev.org/cgi/doi/10.1101/gad.1538207
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