Prp8 impacts cryptic but not alternative splicing frequency.

Pre-mRNA splicing must occur with extremely high fidelity. Spliceosomes assemble onto pre-mRNA guided by specific sequences (5' splice site, 3' splice site, and branchpoint). When splice sites are mutated, as in many hereditary diseases, the spliceosome can aberrantly select nearby pseudo- or "cryptic" splice sites, often resulting in nonfunctional protein.

SNRP-27, the homolog of the tri-snRNP 27K protein, has a role in 5' splice site positioning in the spliceosome.

The tri-snRNP 27K protein is a component of the human U4/U6-U5 tri-snRNP and contains an N-terminal phosphorylated RS domain. In a forward genetic screen in , we previously identified a dominant mutation, M141T, in the highly-conserved C-terminal region of this protein. The mutant allele promotes changes in cryptic 5' splice site choice.