The survival of motor neurons (SMN) complex binds to Sm proteins and small nuclear RNAs (snRNAs) in the cytoplasm. Sm is part the SMN multiprotein complex that contains Gemins 2 – 7, including the DEAD-box RNA helicase Gemin3. The binding of the SMN complex to the snRNAs depends on the presence of specific, high-affinity (nanomolar) binding domains in the snRNAs. The SMN complex binds the Sm proteins through the Sm domains interaction with the Gemins, the TUDOR domain, and through unique arginine- and glycine-rich (RG) domains found in three of these, SmB, SmD1 and SmD3. The association with RG domains is strongly enhanced by the post-translational symmetric dimethylation of specific arginines in these domains, a process that is carried out by the methylosome (JBP1 or PRMT5) complex.