Component of nuclear coiled bodies, also known as Cajal bodies or CBs, which are involved in the modification and assembly of nucleoplasmic snRNPs. Interacts with ANKS1B. Interacts with SMN1 (via Tudor domain). Interacts (via C-terminus) with AK6. Interacts with WRAP53/TCAB1. Interacts with HMBOX1. Interacts with PSME3; the interaction is inhibited by PSME3IP1. Detectable in all tissues analyzed, with the highest levels in brain and testis. The atypical Tudor domain at the C-terminus contains two large unstructured loops, and does not bind methylated residues. Symmetrical dimethylation of arginine residues within the RG repeat region enhances affinity for SMN, and thus localization of SMN complexes to CBs. Phosphorylation during mitosis is associated with disassembly of CBs. Belongs to the coilin family.