Component of the spliceosome A complex. Regulates alternative splicing of a number of mRNAs. May modulate splice site pairing after recruitment of the U1 and U2 snRNPs to the 5' and 3' splice sites of the intron. May both positively and negatively regulate apoptosis by regulating the alternative splicing of several genes involved in this process, including FAS and CASP2/caspase-2. In the case of FAS, promotes production of a soluble form of FAS that inhibits apoptosis. In the case of CASP2/caspase-2, promotes production of a catalytically active form of CASP2/Caspase-2 that induces apoptosis (By similarity). Component of the spliceosome A complex (also known as the prespliceosome). Appears to dissociate from the spliceosome upon formation of the spliceosome B complex (also known as the precatalytic spliceosome), in which the heterotrimeric U4/U6.U5 snRNPs are bound. Interacts with U2AF2; this interaction is direct. Also interacts with ACIN1, PRPF8, SFRS3, SNRPB, SNRPN, SNRNP70 and SNRNP200; these interactions may be indirect (By similarity). Belongs to the RBM5/RBM10 family.