Coilin is the signature protein of the Cajal body (CB), a nuclear suborganelle 
involved in the biogenesis of small nuclear ribonucleoproteins (snRNPs). Newly 
imported Sm-class snRNPs are thought to traffic through CBs before proceeding to 
their final nuclear destinations. Loss of coilin function in mice leads to 
significant viability and fertility problems. Coilin interacts directly with the 
spinal muscular atrophy (SMA) protein via dimethylarginine residues in its 
C-terminal domain. Although coilin hypomethylation results in delocalization of 
survival of motor neurons (SMN) from CBs, high concentrations of snRNPs remain 
within these structures. Thus, CBs appear to be involved in snRNP maturation, 
but factors that tether snRNPs to CBs have not been described. In this report, 
we demonstrate that the coilin C-terminal domain binds directly to various Sm 
and Lsm proteins via their Sm motifs. We show that the region of coilin 
responsible for this binding activity is separable from that which binds to SMN. 
Interestingly, U2, U4, U5, and U6 snRNPs interact with the coilin C-terminal 
domain in a glutathione S-transferase (GST)-pulldown assay, whereas U1 and U7 
snRNPs do not. Thus, the ability to interact with free Sm (and Lsm) proteins as 
well as with intact snRNPs, indicates that coilin and CBs may facilitate the 
modification of newly formed snRNPs, the regeneration of 'mature' snRNPs, or the 
reclamation of unassembled snRNP components.