Molecular functions of the SMN complex.

The SMN complex is essential for the biogenesis of spliceosomal small nuclear ribonucleoproteins and likely functions in the assembly, metabolism, and transport of a diverse number of other ribonucleoproteins. Specifically, the SMN complex assembles 7 Sm proteins into a core structure around a highly conserved sequence of ribonucleic acid (RNA) found in small nuclear RNAs. The complex recognizes specific sequences and structural features of small nuclear RNAs and Sm proteins and assembles small nuclear ribonucleoproteins in a stepwise fashion. In addition to the SMN protein, the SMN complex contains 7 additional proteins known as Gemin2-8, each likely to play a role in ribonucleoprotein biogenesis. This review focuses on the current understanding of the mechanism of the role of the SMN complex in small nuclear ribonucleoprotein assembly and considers the relationship of this function to spinal muscular atrophy.