This domain incorporates the interacting site for the U6-snRNA as part of the U4/U6.U5 tri-snRNPs complex of the spliceosome, and is the prime candidate for the role of cofactor for the spliceosome's RNA core. The essential spliceosomal protein Prp8 interacts with U5 and U6 snRNAs and with specific pre-mRNA sequences that participate in catalysis. 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 [1].

1: 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