LA AUTOANTIGEN ENHANCES AND CORRECTS ABERRANT TRANSLATION OF POLIOVIRUS RNA IN RETICULOCYTE LYSATE

Translation initiation on poliovirus RNA occurs by internal binding of ribosomes to a sequence within the 5' untranslated region. We have pr eviously characterized a HeLa cell protein, p52, that binds to a fragm ent of the poliovirus 5' untranslated region (K. Meerovitch, J. Pellet ier, and N. Sonenberg, Genes Dev. 3:1026-1034, 1989). Here we report t he purification of the HeLa p52. Protein microsequencing identified p5 2 as La autoantigen. The La protein is a human antigen that is recogni zed by antibodies from patients with autoimmune disorders such as syst emic lupus erythematosus and Sjogren's syndrome. We show that the La p rotein stimulates translation of poliovirus RNA, but not brome mosaic virus, tobacco mosaic virus, and alfalfa mosaic virus 4 RNA, translati on in a reticulocyte lysate. In addition, La corrects aberrant transla tion of poliovirus RNA in a reticulocyte lysate. Subcellular immunoloc alization showed that La protein is mainly nuclear, but after poliovir us infection, La is redistributed to the cytoplasm. Our results sugges t that La protein is involved in poliovirus internal initiation of tra nslation and might function through a similar mechanism in the transla tion of cellular mRNAs.