Pre-messenger RNA splicing is a two-step process by which introns are removed and exons joined together. In yeast, the U5 snRNA loop 1 interacts with the 5' exon before the first step of splicing and with the 5' and 3' exons before the second step. In vitro studies revealed that yeast U5 loop 1 is not required for the first step of splicing but is essential for holding the 5' and 3' exons for ligation during the second step. It is critical, therefore, that loop 1 contacts the 5' exon before the first step of splicing to hold this exon following cleavage from the pre-mRNA. At present it is not known how U5 loop 1 is positioned on the 5' exon prior to the first step of splicing. To address this question, we have used site-specific photoactivated crosslinking in yeast spliceosomes to investigate the interaction of U5 loop 1 with the pre-mRNA prior to the first step of splicing. We have found that the highly conserved uridines in loop 1 make ATP-dependent contacts with an approximately 8-nt region at the 5' splice site that includes the invariant GU. These interactions are dependent on functional U2 and U6 snRNAs. Our results support a model where U5 snRNA loop 1 interacts with the 5' exon in two steps during its targeting to the 5' splice site.
|Evidence ID||Analyze ID||Interactor||Interactor Systematic Name||Interactor||Interactor Systematic Name||Type||Assay||Annotation||Action||Modification||Phenotype||Source||Reference||Note|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Gene Ontology Term||Gene Ontology Term ID||Qualifier||Aspect||Method||Evidence||Source||Assigned On||Reference||Annotation Extension|
|Evidence ID||Analyze ID||Gene||Gene Systematic Name||Phenotype||Experiment Type||Experiment Type Category||Mutant Information||Strain Background||Chemical||Details||Reference|
|Evidence ID||Analyze ID||Regulator||Regulator Systematic Name||Target||Target Systematic Name||Experiment||Conditions||Strain||Source||Reference|