PURIFICATION, MICROSEQUENCING, AND IMMUNOLOCALIZATION OF P36, A NEW INTERFERON-ALPHA-INDUCED PROTEIN THAT IS ASSOCIATED WITH HUMAN LUPUS INCLUSIONS

The trace interferon-alpha induced protein, p36, was induced in Raji c ells in association with lupus inclusions. It was solubilized in a non ionic detergent buffer, enriched by differential centrifugation and by preparative isoelectric focusing, and purified to homogeneity on two- dimensional protein gels. Failure to obtain N-terminal amino acid sequ ence, however, suggested a blocked alpha-amino group. Sequences of six tryptic peptides, 13-19 amino acids in length, were obtained after di gestion, microbore-high performance liquid chromotography purification , and chemical sequence analysis. None of the six sequences, which rep resented approximately 25% of the entire protein, shared any meaningfu l homologies with entries in protein sequence repositories. Raji-cell p36 was shown in Western blots with antipeptide antibodies to be induc ed at least 400-fold and by immunofluorescence microscopy to co-locali ze with the endoplasmic reticulum resident protein, protein disulfide isomerase. These results show that p36 is a new interferon-alpha-induc ed protein that localizes in the endoplasmic reticulum, the cell regio n in which the lupus inclusions form, and that p36 is probably physica lly associated with the lupus inclusions.