Figure 3. Role of PRPF31 in pre-mRNA splicing. PRPF31 is a splicing factor specific to the U4/U6 snRNP, and its primary role is to recruit and physically tether U5 to U4/U6 to yield the U4/U6+U5 tri-snRNP. This involves an interaction between PRPF31 and the U5-specific splicing factor PRPF6. Once incorporated into the spliceosomal complex B, activation involves loss of U1 and U4 and all tri-snRNP associated proteins, including PRPF31 and PRPF6. The mutant PRPF31 proteins are predicted to inhibit this activation step (marked with crosses) and prevent recycling of spliceosomal components for future splicing events.