hPrp3p (human pre-mRNA splicing factor 3) was identified as a factor that associated with U4/U6 snRNPs which are components of the splicesome. hPrp3p is homologous to S. cerevisiae splicing factor Prp3p. Mutations in the PRPF3 gene are associated with retinitis pigmentosa-18. It has been determined that mutations in hPrp3p may alter the recognition motif for phosphorylation by casein kinase II (CKII) and that loss of phosphorylation may result in aberrant interactions within the U4/U6 snRNP complex.