In vitro interaction of U2 snRNA with cytoplasmic 6S protein complexes

Interactions of U2 snRNA with anti-Sm precipitable proteins in RNA-free cytoplasmic complexes were analyzed. U2 snRNA was found to bind specifically with proteins in the 6S complexes but not in the 20S complexes. The binding activity was preserved using U2 snRNA having a mutated Sm binding site. Label-transfer experiments indicate that snRNA makes direct contact with anti-Sm precipitable proteins in the 6S fraction with apparent molecular mass of about 16 kDa. These data corroborate that proteins in the 6S core particle are the first to interact with snRNA, and suggest that the proteins recognize snRNA structures in addition to the Sm site.