Gemin5, a novel WD repeat protein component of the SMN complex that binds Sm proteins

The survival of motor neurons (SMN) protein is the product of the disease gene of spinal muscular atrophy and is found both in the cytoplasm and the nucleus, where it is concentrated in gems. SMN is part of a multi-protein complex that includes Gemin2, Gemin3, and Gemin4. The SMN complex plays an important role in the cytoplasmic assembly of small nuclear ribonucleoproteins (snRNPs) and likely other RNPs in pre-mRNA splicing and in the assembly of transcriptosomes. Here, we report the identification of an additional component of the SMN complex, a novel WD repeat protein termed Gemin5. Gemin5 binds SMN directly and is a component of the SMN complex. Furthermore, Gemin5 interacts with several of the snRNP core proteins including SmB, SmD1, SmD2, SmD3, and SmE, suggesting that it participates in the activities of the SMN complex in snRNP assembly. Immunolocalization studies demonstrate that Gemin5 is found in the cytoplasm and in the nucleus, where it colocalizes with SMN in gems. The presence of 13 WD repeat domains in the amino-terminal half of Gemin5 and a coiled-coil motif near its carboxyl terminus indicate that it may form a large heteromeric complex and engage in multiple interactions.