Involved in spliceosome assembly. Associates with spliceosomes (PubMed:11331295). Associates with U4/U5/U6 tri-snRNP and with U2 snRNP (PubMed:11331295). Interacts (via Tudor domain) with SNRPD3 (via C-terminus); the interaction is direct (PubMed:22101937). Detected in nuclear speckles containing snRNP and in Cajal (coiled) bodies. Detected at intermediate levels in skeletal muscle, and at low levels in heart and pancreas. The Tudor domain mediates association with dimethylarginines, which are common in snRNP proteins. Belongs to the SMN family.