Required for efficient splicing and pre-mRNA nuclear retention. May also be involved in positioning the proximal bud pole signal. Belongs to the pre-mRNA retention and splicing (RES) complex composed of at least BUD13, IST3 and PML1. May also belong to the CWC complex (or CEF1-associated complex) composed of the U2, U5 and U6 snRNAs and at least BUD13, BUD31, BRR2, CDC40, CEF1, CLF1, CUS1, CWC2, CWC15, CWC21, CWC22, CWC23, CWC24, CWC25, CWC27, ECM2, HSH155, IST3, ISY1, LEA1, MSL1, NTC20, PRP8, PRP9, PRP11, PRP19, PRP21, PRP22, PRP45, PRP46, SLU7, SMB1, SMD1, SMD2, SMD3, SMX2, SMX3, SNT309, SNU114, SPP2, SYF1, SYF2, RSE1 and YJU2. Interacts with IST3 and PML1. Belongs to the CWC26 family.