Ro ribonucleoprotein assembly in vitro. Identification of RNA-protein and protein-protein interactions.

The human Y RNAs, small RNAs with an unknown function, are complexed with at least three proteins: the 60,000 M(r) Ro protein (Ro60), the 52,000 M(r) Ro protein (Ro52) and the La protein (La). In this study we examined the intermolecular interactions between the components of these so-called Ro ribonucleoprotein (Ro RNP) complexes. Incubation of 32P-labelled hY1 RNA in HeLa S100 extract allows the reconstitution of Ro RNP complexes, which were analysed by immunoprecipitation with monospecific antisera. By immunodepletion of HeLa S100 extracts for either Ro60, Ro52 or La, followed by supplementation with recombinant Ro60 or La, it was demonstrated that both Ro60 and La bind to hY1 RNA directly without being influenced by one of the other proteins. However, binding of Ro52 to hY1 RNA required the presence of Ro60, which strongly suggests that the association of Ro52 with Ro RNPs is mediated by protein-protein interactions between Ro60 and Ro52.