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

Abstract

The small adenovirus-encoded VA RNA occur as ribonucleoprotein (RNP) particles in association with a cellular protein antigen, La, recognized by the anti-La class of lupus sera. The La antigen was tentatively identified as a [human cervical carcinoma] HeLa cell phosphoprotein of MW .apprx. 45,000, present in infected and uninfected cells. The antigen appears not to be required for the transcription of VA RNA in vitro. RNP particles that contain newly synthesized VA RNA 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 base-paired stem, but structures of comparable stability cannot be formed by the chimeric variant molecules. Thus, the recognition site is probably the terminal nucleotides themselves rather than the stem structure.