Predicted to be involved in generation of catalytic spliceosome for second transesterification step. Predicted to act upstream of or within RNA splicing and mRNA processing. Predicted to be located in nuclear speck. Predicted to be part of U2-type post-spliceosomal complex; U4/U6 x U5 tri-snRNP complex; and U5 snRNP. Orthologous to human PRPF18 (pre-mRNA processing factor 18).