Structure and function of small ribonucleoproteins from eukaryotic cells.

Autoantibodies from patients with systemic lupus erythematosus and other related diseases have been used to identify and study small RNA-protein complexes from mammalian cells. Properties of three previously described and several new classes of small ribonucleoproteins (RNPs) are reviewed. The sequence of Drosophila U1 RNA reveals that the region proposed to pair with 5' splice junctions is conserved, while that proposed to interact with 3' junctions diverges; this forces some revision of the model for U1 small nuclear (sn)RNP participation in hnRNA splicing. Further characterization of the Ro and La small RNPs has shown that the Ro small cytoplasmic (sc)RNPs are a subclass of La RNPs. Both tRNA and 5S rRNA precursors are at least transiently associated with the La protein. This raises the possibility that the La protein may be an RNA polymerase III transcription factor.