The pre-mRNA splicing occurs in spliceosomes, which consist of four ribonucleoprotein (snRNP) particles (U1, U2, U5 and U4/U6) and more than fifty proteins. This U4/U6-associated splicing factor, Hprp3p, is a 77 kDa protein, which is homologous to the Saccharomyces cerevisiae splicing factor Prp3p and may play a role in spliceosome assembly. Western blot analysis of HeLa cell nuclear extracts detected PRP3 protein at an apparent molecular mass of about 90 kD(PMID: 9328476 ). The discrepancy between the molecular mass reported here and that predicted from the Hprp3p coding sequence can be attributed, at least partially, to the highly positive charge; its value of predicted isoelectric point (IP) is ∼9.99. This antibody is a rabbit polyclonal antibody raised against an internal region of human PRPF3. A predicted molecular mass of 77 kDa and the gene is named PRPF3 because it is homologous to the yeast PRP3 gene. We noticed that although the predicted molecular mass of PRPF3 is77 kDa, the protein produced in E.coli migrated like a 90 kDa protein in SDS-PAGE. (PMID: 9328476)