Probable ubiquitin-protein ligase which is mainly involved pre-mRNA splicing and DNA repair. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Homotetramer. Component of the multiprotein assembly MOS4-associated complex (MAC) at least composed of MOS4, CDC5, PRL1 and PRP19 which is related to the PRP19C/Prp19 complex/NTC/Nineteen complex identified in other organisms. Associated with the spliceosome. Belongs to the WD repeat PRP19 family.