On the Biochemical Nature of the ‘Sm’ Nucleoplasmic Antigen

Abstract

The nucleoplasmic autoantigens RNP and Sm are of particular interest because of their associations with certain symptoms of mixed connective tissue disease and systemic lupus erythematosus. The RNP is generally thought to be a ribonucleoprotein and there is evidence that its RNA may be single-stranded. Experiments presented in this report are in support of the concept that the Sm-antigen may also be an RNA protein. Purified Sm-anti-Sm precipitates were shown to have high RNA contents and treatment of Sm-antigen with RNAase in a hypotonic medium strongly reduced in antigenicity. The latter effect indicates that the Sm-antigen may in contrast to the RNP contain double-stranded RNA, a possibility also suggested by the finding that the Sm-antigen was soluble in 2 M LiCl. The Sm-antigen was found further to differ from RNP in being selectively absorbed in BD-Sephadex, while RNP remained active in the supernatant. Cytochemical studies involving stimulation and inhibition experiments with lectins and RNA polymerase inhibitors showed that the Sm-antigen was, in distinction to RNP, sensitive to rifampicin but not to alpha-amanitine. This suggests that the RNAs of the nucleoplasmic antigens may be synthesized by different RNA polymerases.

Detection of autoantibodies to Sm antigen in systemic lupus erythematosus by immunodiffusion, ELISA and immunoblotting: variability of incidence related to assays and ethnic origin of patients

“…Calf thymus extract (CTE) was prepared according to Abuaf et al [ min of incubation, the extract was centrifuged for 20 min at 2500 g. The pellet was discarded and the concentration of PEG in the supernatant raised to After a 20 min centrifugation at 2500 g the precipitate was collected and dissolved with 0.01 5 rnol I -I PB8. [13]. PB8-dialysed CTE (80 ml) or PEG-treated CTE was layered on the top of a chromatography column, packed with 75 ml of Blue Sepharose CL-6B (Pharmacia, Uppsala, Sweden) and equilibrated with PB8.…”

The composition of the nuclear antigens Sm and RNP of human rheumatic and connective tissue diseases and the relevance of their autoantibodies as probes for RNA processing mechanisms

“…It has been concluded that these sites are the same as those involved in the forms of the antigens described in table 2 and, if so, these results contrast with some of the established properties of Sm and RNP. For example, both Sm and RNP can be found to be sensitive to protease and ribonuclease [9,36], indicating that the antigenic determinant sites contain protein and RNA. An alternative view has now been put that the RNA is simply acting as a carrier for the protein determinant [23].…”