Characterization of autoantibodies that recognize U4/U6 small ribonucleoprotein particles in serum from a patient with primary Sjögren's syndrome.
We identified autoantibodies that recognize the U4/U6 snRNPs in a serum from a 63-year-old Japanese patient (TT) with primary Sjögren's syndrome. This patient's serum immunoprecipitated U4 and U6 sn-RNAs exclusively from 32P-labeled HeLa cell extracts and a newly identified 120-kDa protein along with the Sm core proteins (B'/B, D, E, F, and G) from [35S] methionine-labeled HeLa cell extracts. Immunoblotting demonstrated that only the 120-kDa protein was recognized by this unique serum. In glycerol density gradient centrifugation, the 120-kDa protein reactive with TT serum cosedimented with U4 and U6 snRNAs, suggesting that the 120-kDa protein is a unique component of the U4/U6 snRNP particle. In the same study, the U4/U6 snRNP precipitated by TT serum sedimented only in the lower density, whereas anti-Sm antibodies precipitated U4/U6 snRNAs in a broad range of the gradient. This result suggests the presence of at least two molecular forms of the U4/U6 snRNP particles; larger particles, probably the U4/U5/U6 snRNP complex, and free particles. Thus, the U4/U6 snRNP recognized by TT serum includes the U4 and U6 snRNAs, with Sm core proteins, and the novel 120-kDa protein, and appears to be a free particle not associated with larger complexes.
Fujii
T
T
Department of Internal Medicine, Keio University School of Medicine, Tokyo, Japan.
Mimori
T
T
Hama
N
N
Suwa
A
A
Akizuki
M
M
Tojo
T
T
Homma
M
M
D001323:Autoantibodies / Q000097:blood* / Q000302:isolation & purification; D005260:Female; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D008875:Middle Aged; D012342:RNA, Small Nuclear / Q000276:immunology; D012261:Ribonucleoproteins / Q000096:biosynthesis / Q000276:immunology*; D017411:Ribonucleoproteins, Small Nuclear; D012859:Sjogren's Syndrome / Q000097:blood* / Q000276:immunology*
D001323:Autoantibodies; D012342:RNA, Small Nuclear; D012261:Ribonucleoproteins; D017411:Ribonucleoproteins, Small Nuclear