Subcellular distribution of Ro ribonucleoprotein complexes and their constituents.

Ro ribonucleoprotein particles (Ro RNPs) are complexes of several proteins with a small RNA polymerase III-transcribed Ro RNA. Despite their relative abundance and evolutionary conservation no function has as yet been ascribed to these complexes. Also their subcellular distribution is still largely unknown as immunofluorescence studies concerning their localization have produced conflicting data. We have used cell enucleation to fractionate cells into cytoplasmic and nuclear fractions. Analysis of these fractions revealed an exclusively cytoplasmic localization for the Ro RNPs. The majority of the Ro RNAs are shown to be stably associated with all three known Ro RNP proteins. Although no Ro RNAs could be detected in the nuclear fraction, the Ro RNP-specific proteins were abundantly present. These nuclear non-Ro RNA-associated proteins are shown to be capable of binding Ro RNAs.