Missense mutation clustering in the survival motor neuron gene: a role for a conserved tyrosine and glycine rich region of the protein in RNA metabolism?

The Survival Motor Neuron (SMN) gene shows deletions in the majority ofpatients with Spinal Muscular Atrophy (SMA), a disease of motor neurondegeneration. To date only two missense mutations have been reported in SMNin patients with SMA. The fact that no SMN-homologues have been forthcomingfrom data-base searching has resulted in a lack of hypotheses concerningthe structural and functional consequences of these mutations. Recently SMNhas been shown to interact with heterogeneous nuclear ribonucleoproteins(hnRNPs) suggesting a role in mRNA metabolism. We describe a novel missensemutation and the subsequent identification of a triplicatedtyrosine-glycine (Y-G) peptide sequence at the C-terminal of SMN whichencompasses each of the three predicted amino acid sequence substitutions.We have identified apparent orthologues of SMN in Caenorhabditis elegansand Schizosaccharomyces pombe. These sequences retain the highly conservedY-G motif and provide additional support for a role of SMN in mRNAmetabolism.