Involved in pre-mRNA splicing as a component of the splicing factor SF3B complex (PubMed:27720643). SF3B complex is required for 'A' complex assembly formed by the stable binding of U2 snRNP to the branchpoint sequence (BPS) in pre-mRNA. Sequence independent binding of SF3A/SF3B complex upstream of the branch site is essential, it may anchor U2 snRNP to the pre-mRNA (PubMed:12234937). May also be involved in the assembly of the 'E' complex (PubMed:10882114). Belongs also to the minor U12-dependent spliceosome, which is involved in the splicing of rare class of nuclear pre-mRNA intron (PubMed:15146077). Identified in the spliceosome C complex (PubMed:11991638). Component of the U11/U12 snRNPs that are part of the U12-type spliceosome (PubMed:15146077). Component of splicing factor SF3B which is composed of at least eight subunits; SF3B1, SF3B2, SF3B3, SF3B4, SF3B5, SF3B6, PHF5A and DDX42 (PubMed:12234937, PubMed:12738865, PubMed:27720643, PubMed:28541300). SF3B associates with the splicing factor SF3A and a 12S RNA unit to form the U2 small nuclear ribonucleoproteins complex (U2 snRNP) (PubMed:12234937). Interacts directly with SF3B4 (PubMed:25737013). The SF3B complex composed of SF3B1, SF3B2, SF3B3, SF3B4, SF3B5, SF3B6 and PHF5A interacts with U2AF2 (PubMed:27720643). Found in a complex with PRMT9, SF3B2 and SF3B4 (PubMed:25737013). Interacts (Arg-508-methylated form) with SMN1 (via Tudor domain) (PubMed:25737013). Interacts with RBM7 (PubMed:27905398). Interacts with ERCC6 (PubMed:26030138). (Microbial infection) Interacts with HIV-1 Vpr. Methylation at Arg-508 by PRMT9 is required for the interaction with SMN1. Truncated N-terminus. Contaminating sequence. Potential poly-A sequence. Truncated N-terminus.