U5 snRNA interacts with exon sequences at 5' and 3' splice sites

Area of Science:

• Molecular Biology
• RNA Biology
• Genetics

Background:

• U5 small nuclear RNA (snRNA) is a crucial component of the spliceosome, essential for pre-mRNA splicing.
• The precise function of U5 snRNA, particularly its loop sequence, in the splicing mechanism remains largely unknown.
• Previous studies indicate potential roles in splice site recognition and catalytic steps of splicing.

Purpose of the Study:

• To investigate the role of specific mutations in the yeast U5 snRNA loop sequence.
• To elucidate how these mutations affect pre-mRNA cleavage at aberrant 5' splice sites.
• To understand the mechanism by which U5 snRNA mutations facilitate the processing of dead-end lariat intermediates.

Main Methods:

• Site-directed mutagenesis of the yeast U5 snRNA loop sequence.
• Analysis of pre-mRNA cleavage products and splicing intermediates using molecular assays.
• RNA-RNA base-pairing analysis to identify interactions between U5 snRNA and pre-mRNA.

Main Results:

• Specific U5 snRNA loop mutations activate cleavage of mutant pre-mRNAs at aberrant 5' splice sites.
• Activation of aberrant cleavage involves base pairing between U5 snRNA and upstream pre-mRNA sequences.
• Mutations facilitate the conversion of dead-end lariat intermediates to mRNA, correlating with U5 snRNA base pairing to exon 2.

Conclusions:

• The U5 snRNA loop sequence is intimately involved in the transesterification reactions at both 5' and 3' splice sites.
• The observed interactions resemble exon recognition in group II self-splicing introns.
• These findings support the hypothesis that U5 snRNA may have evolved from a functional domain of a group II-like intron.