Interaction between VA RNA and the lupus antigen La: formation of a ribonucleoprotein particle in vitro.

The small adenovirus-encoded VA RNAs occur as ribonucleoprotein (RNP) particles in association with a cellular protein antigen, La, recognized by the anti-La class of lupus sera [Lerner, M. R., Boyle, J. A., Hardin, J. A. & Steitz, J. A. (1981) Science 211, 400-402]. We have tentatively identified the La antigen as a HeLa cell phosphoprotein of Mr approximately equal to 45,000, present in infected and uninfected cells. The antigen appears not to be required for the transcription of VA RNAs in vitro. RNP particles that contain newly synthesized VA RNAs assemble rapidly in transcription extracts making VA RNA and also can be reconstituted from purified VA RNA and a source of La antigen. Variant forms of VA RNAI with sequence deletions and substitutions bind to the La antigen, suggesting that the recognition site includes the RNA termini or the sequences corresponding to the internal control region (promoter), or both. Upon reconstitution with fragments of VA RNAI, oligonucleotides from both the 5' and 3' termini bind to the antigen, but those from the control region do not. The terminal oligonucleotides of wild-type VA RNA can form a basepaired stem, but structures of comparable stability cannot be formed by the chimeric variant molecules. Therefore, the recognition site is probably the terminal nucleotides themselves rather than the stem structure.