Isolation and characterization of a new 110 kDa human nuclear RNA- binding protein (p110(nrb))

RNA-protein interactions play key roles in many fundamental cellular processes such as RNA processing, RNA transport, and RNA translation. During our attempts to isolate the human U6 small nuclear RNA capping enzyme, we identified a new 110 kDa nuclear RNA-binding protein, designated p110(nrb). The full-length cDNA clone for p110(nrb) was characterized, and it encodes a 963 amino acid polypeptide. It is a highly acidic protein (pI 5.28) and the carboxyl terminal portion contains two conserved RNP motifs. A databank search found a putative C. elegans protein that might be the p110(nrb) homologue. The p110(nrb) was overexpressed as a glutathione S-transferase fusion protein in insect Sf9 cells, purified by affinity chromatography and injected into rabbits to produce specific polyclonal antibodies. Immunofluorescent staining showed that p110(nrb) is distributed evenly throughout the nucleoplasm. Northern blots showed that the mRNA is expressed in all tissues examined. An in vitro RNA-binding assay showed that p110(nrb) bound to RNA. These data suggest that p110(nrb) may play a role in the metabolism of nuclear RNA.