Alu RNA-protein complexes formed in vitro react with a novel lupus autoantibody

We have screened sera from patients with systemic lupus erythematosus for reactivity with RNA transcribed in vitro using HeLa whole cell extracts. Sera from 14 out of 114 patients precipitated an RNA transcribed by RNA polymerase III from a plasmid containing an Alu family sequence (i.e. the repetitive DNA sequence that is cut by the Alu restriction enzyme) located upstream from the human gamma G-globin gene. These Alu transcripts were not precipitated by anti-La, anti-Sm, anti-RNP or anti-Ro antibodies, suggesting that Alu RNA was precipitated by a previously undescribed lupus specificity. Analysis of [35S]methionine-labeled immunoprecipitates indicated that Alu RNA binds a protein of about 68 kDa. This protein may be Alu specific since three different Alu transcripts were precipitated by the anti-Alu sera whereas another RNA polymerase III transcript, adenovirus VA I RNA, was not precipitated by the same sera.