Prp8 impacts cryptic but not alternative splicing frequency

Pre-mRNA splicingmust occur with extremely high fidelity. Spliceosomesassemble onto pre-mRNA guided by specific sequences (5′ splicesite, 3′ splicesite, and branchpoint). When splicesites are mutated, as in many hereditary diseases, the spliceosomecan aberrantly select nearby pseudo- or “cryptic” splicesites, often resulting in nonfunctional protein. How the spliceosomedistinguishes authentic splicesites from cryptic splicesites is poorly understood. We performed a Caenorhabditis elegans genetic screento find cellular factors that affect the frequency with which the spliceosomeuses cryptic splicesites and identified two alleles in core spliceosomecomponent Prp8 that alter cryptic splicingfrequency. Subsequent complementary genetic and structural analyses in yeast implicate these alleles in the stability of the spliceosome’s catalytic core. However, despite a clear effect on cryptic splicing, high-throughput mRNA sequencing of these prp-8 mutant C. elegans reveals that overall alternative splicingpatterns are relatively unchanged. Our data suggest the spliceosomeevolved intrinsic mechanisms to reduce the occurrence of cryptic splicingand that these mechanisms are distinct from those that impact alternative splicing.