The La or
SS-B antigen is associated with
rheumatic diseases,
systemic lupus erythematosus, and
Sjogren's syndrome, and is part of a larger
ribonucleoprotein complex. Immunoaffinity chromatography allowed for the efficient separation of the
La antigen from the bulk of the cellular
proteins, with a minimum of
protease exposure.
Protein blot analysis of the affinity-isolated material indicated a major immunoreactive
polypeptide of 50,000 m.w. A comparison of this
antigen in a number of mammalian sources (human, rabbit, and rat) suggested strong conservation of the native
polypeptide m.w. Likewise, in a direct comparison of this
antigen from Epstein-Barr virus-infected cells in which there are distinct differences in the
antigen-associated
RNA species, the immunoreactive
polypeptide species were of similar size. The La
protein is readily susceptible to endogenous proteolysis, with the resulting generation of smaller, discrete
polypeptides that still retain antigenicity. By using the La
protein to monitor potential degradation, we have developed a simple two-step procedure to isolate the La-associated
snRNP complex. The complexes thus isolated provide material suitable as a source of both the active
antigen and of the functional
ribonucleoprotein complex.