Component of the U5 snRNP complex that is required for spliceosome assembly and for pre-mRNA splicing. Involved in splicing pre-mRNA of the A1 cistron and other genes that are important for cell growth. Heterodimer (Probable). Interacts with PRP8 (via RNase H homology domain and MPN domain), competing with BRR2 for the same binding site. Component of a U5 snRNP complex that contains at least the U5 snRNA, PRP8, SNU114, AAR2, SMB1, SMD1, SMD2, SMD3, SME1, SMX2 and SMX3, but is not a component of the U4/U6-U5 tri-snRNP complex. This protein lacks a nuclear localization signal, it may interact in the cytoplasm with a component of spliceosomes via the leucine-zipper and then be transported into the nucleus. Phosphorylated on serine and tyrosine residues. Present with 7330 molecules/cell in log phase SD medium. Belongs to the AAR2 family.