Retinitis pigmentosa (RP) is an inheritable disease characterized by progressive retinal degeneration and loss of rod photoreceptor cells, leading to total blindness. Recently three genes responsible for autosomal dominant RP (HPRP3, PRPF31, and PRPC8) have been identified as the human orthologues of the yeast genes PRP3, PRP31, and PRP8, respectively. The removal of introns from nuclear pre-mRNAs occurs on spliceosomes, which consist of 4 small nuclear ribonucleoprotein (snRNP) particles and a number of transiently associated splicing factors. All three PRP (pre-mRNA processing factor) genes are involved in the function of the U4/U6,U5 tri-snRNP, the spliceosome component required for the transition to a catalytically active state. In mammals, the 63 kDa HPRP3 is thought to recruit HPRP4 to the U4/U6 snRNP. In yeast, PRP3 and PRP4 genetically interact, and physical interactions between Prp3p and Prp4p proteins are required for association of Prp3p and Prp4p with U4/U6.Synonyms: HPRP3, PRP3, Pre-mRNA-splicing factor 3, U4/U6 small nuclear ribonucleoprotein Prp3, U4/U6 snRNP 90 kDa protein