The essential spliceosomal protein Prp8 interacts with U5 and U6 snRNAs and with specific pre-mRNA sequences that participate in catalysis [1]. This close association with crucial RNA sequences, together with extensive genetic evidence, suggests that Prp8 could directly affect the function of the catalytic core, perhaps acting as a splicing cofactor [2].

1: Prp8 protein: at the heart of the spliceosome. Grainger RJ, Beggs JD; RNA. 2005;11:533-557. PMID:15840809

2: Dissection of Prp8 protein defines multiple interactions with crucial RNA sequences in the catalytic core of the spliceosome. Turner IA, Norman CM, Churcher MJ, Newman AJ; RNA. 2006;12:375-386. PMID:16431982