Probable ubiquitin-protein ligase involved in pre-mRNA splicing. Acts as a central component of the NTC complex (or PRP19-associated complex) that associates to the spliceosome to mediate conformational rearrangement or to stabilize the structure of the spliceosome after U4 snRNA dissociation, which leads to spliceosome maturation. It is also probably involved in 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 NTC complex (or PRP19-associated complex), composed of at least CEF1, CLF1, ISY1, NTC20, SNT309, SYF1, SYF2, and PRP19. The NTC complex associates with the spliceosome after the release of the U1 and U4 snRNAs and forms the CWC spliceosome subcomplex (or CEF1-associated complex) reminiscent of a late-stage spliceosome composed also of the U2, U5 and U6 snRNAs and at least BUD13, BUD31, BRR2, CDC40, CUS1, CWC2, CWC15, CWC21, CWC22, CWC23, CWC24, CWC25, CWC27, ECM2, HSH155, IST3, LEA1, MSL1, PRP8, PRP9, PRP11, PRP21, PRP22, PRP45, PRP46, SLU7, SMB1, SMD1, SMD2, SMD3, SMX2, SMX3, SNU114, SPP2, RSE1 and YJU2. Interacts with CLF1, ISY1, NTC20, PRP19, PRP46, SYF1 and SYF2. Interacts with CWC2. Present with 11700 molecules/cell in log phase SD medium. The tetramer is an elongated particle consisting of four globular WD40 domains held together by a central stalk. Belongs to the WD repeat PRP19 family.