A properly assembled Sm core and the m3G cap structure are prerequisites for small nuclear ribonucleoprotein (snRNP) import into the nucleus. Once imported into the nucleus, the snRNPs are initially concentrated in Cajal bodies (CBs), where there is further processing of the snRNAs plus binding of additional proteins, from CRBs they transit to "speckles", from where they are engaged for pre-mRNA splicing. The SMN complexes in the nucleus are found throughout the nucleoplasm but are particularly concentrated in Gems, the "twins" of the snRNP-rich CBs.