Precursor molecules of both human 5S ribosomal RNA and transfer RNAs are bound by a cellular protein reactive with anti-La lupus antibodies

The small ribonucleoproteins recognized by anti-La autoantibodies contain a heterogeneous mixture of small RNAs from uninfected mammalian cells. The identity of many of these has now been established by the discovery of precursor forms of 5S rRNA and of certain tRNAs among La RNAs from HeLa cells. The small fraction of 5S rRNA molecules that exist as La ribonucleoproteins in vivo possess 1 or 2 additional U residues at their 3' ends. Such 5S molecules bound to the La protein have also been identified with in vitro nuclear transcription systems. Pulse-chase experiments performed both in vivo and in vitro support the idea that most newly synthesized 5S rRNA molecules are transiently associated with the La protein. Cell extracts contain a processing activity that converts longer in vitro-synthesized 5S RNA transcripts into molecules of mature size. The presence of in vivo tRNA precursors in the heterogeneous mixture of La RNAs is demonstrated by the identification of precursor forms of five different specific tRNAs (Meti, Asp, Gly, Glu, Asn). After in vitro transcription of a tRNA gene (tRNAiMet), only products the size of precursor molecules are precipitable by anti-La antibodies. The realization that virtually every known RNA polymerase III product associates at least initially with the La antigen suggests that this protein plays an essential role in the synthesis or maturation of all class III transcripts.

Striking similarities are exhibited by two small Epstein-Barr virus-encoded ribonucleic acids and the adenovirus-associated ribonucleic acids VAI and VAII

The nucleotide sequence of the region of the Epstein-Barr virus genome that specifies two small ribonucleic acids (RNAs), EBER 1 and EBER 2, has been determined. Both of these RNAs are encoded by the right-hand 1,000 base pairs of the EcoRI J fragment of EBV deoxyribonucleic acid. EBER 1 is 166 (167) nucleotides long and EBER 2 is 172 +/- 1 nucleotides long; the heterogeneity resides at the 3' termini. The EBER genes are separated by 161 base pairs and are transcribed from the same deoxyribonucleic acid strand. In vitro, both EBER genes can be transcribed by RNA polymerase III; sequences homologous to previously identified RNA polymerase III intragenic transcription control regions are present. Striking similarities are therefore apparent both between the EBERs and the two adenovirus-associated RNAs, VAI and VAII, and between the regions of the two viral genomes that specify these small RNAs. We have shown that VAII RNA as well as VAI RNA and the EBERs exist in ribonucleoprotein complexes which are precipitable by anti-La antibodies associated with systemic lupus erythematosus. Finally, we have demonstrated that the binding of protein(s) from uninfected cells confers antigenicity on each of the four virus-encoded small RNAs.