Spliceosomal small nuclear ribonucleoproteins in trypanosomes: SMN-directed assembly of Sm core complexes and functional role of core variations

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Spliceosomal small nuclear ribonucleoproteins (snRNPs) consist of a heteroheptameric ringlike Sm core assembled on the Sm binding site of the snRNA and additional, snRNP-specific proteins. Recently we have characterized the first examples of Sm core variations in the U2 and U4 snRNPs, where snRNP-specific Sm subunits replace two or one, respectively, of the canonical Sm subunits. In addition, we have identified the trypanosome SMN ortholog, and obtained initial functional evidence that it is involved in directing snRNA-specific Sm core assembly. Here we plan, first, to study the function of these core variations, focussing on the U4 snRNP. Second, we will biochemically analyze the mechanism of SMN-mediated Sm core assembly in the trypanosome system, using in vitro reconstitution and inducible RNAi knockdown systems. These studies promise new insights in the SMN function in a model, which appears to be much simpler than the multicomponent system of higher eukaryotes.