Mpr1p, Pad1p N-terminal (MPN) domains without isopeptidase activity found in splicing factor Prp8Members of this family are found in pre-mRNA-processing factor 8 (Prp8) which is a critical splicing factor, interacting with several other spliceosomal proteins, snRNAs, and the pre-mRNA, thus organizing and stabilizing the spliceosome catalytic core. Prp8 is one of the largest and most highly conserved of nuclear proteins, occupying a central position in the catalytic core of the spliceosome. Its C-terminal domain exhibits a JAB1/MPN-like core similar to deubiquitinating enzymes, but does not show catalytic isopeptidase activity, possibly because the putative isopeptidase center is covered by insertions and terminal appendices that are grafted onto this core, thus impairing the metal binding site. It is proposed that this domain is a protein interaction domain instead of a Zn(2+)-dependent metalloenzyme as proposed for some MPN proteins. The DEAD-box protein Brr2 and the GTPase Snu114 bind to the Prp8 C-terminus, a region where mutations in human Prp8 (hPrp8) cause a severe form of the genetic disorder retinitis pigmentosa, RP13, which leads to progressive photoreceptor degeneration in the retina and eventual blindness. At the N-terminus of Prp8, there are several domains, including a highly variable nuclear localization signal (NLS) motif rich in prolines, a conserved RNA recognition motif (RRM), and U5 and U6 snRNA binding sites.