Survival motor neuron protein facilitates assembly of stress granules.

The survival motor neuron (SMN) protein forms cytoplasmic granules when overexpressed. We report here that SMN co-localizes with TIA-1/R and G3BP, protein assemblers of stress granules (SGs), and that SMN is co-immunoprecipitated with TIA-1/R, suggesting that SMN granules are SGs. Formation of SMN granules precedes accumulation of TIA-1/R, indicating that SMN serves as a facilitator of SG formation. However, the exon 7 skipping product, SMNDelta7, is largely retained in the nucleus and forms nuclear granules, indicating that exon 7 is critical for SG formation. Our findings reveal a novel SMN function and possible SG involvement in the pathogenesis of spinal muscular atrophy.