RNP-Sm

Native - Calf Thymus

Alternate Names:

U1 snRNP antigen

Uniprot IDs:	Q3ZC10 Q3SZF8 F1MZ00 Q1RMR2 Q32PA0 Q2KIR1
mRNA RefSeq:	NM_001035065 NM_001034476 NM_001076334 NM_001046039 NM_001076046
Protein RefSeq:	NP_001030237 NP_001029648 NP_001069802 NP_001039504 NP_001069514

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Autoantibodies directed against the snRNP (small nuclear ribonucleoprotein) autoantigens referred to as RNP and Sm were originally detected in the sera of systemic lupus erythematosus (SLE) patients1. In mixed connective tissue disease (MCTD), anti-RNP antibodies are found in patient sera at high titre and in the absence of Sm^1,2.

Such autoantibodies are also known to occur in the sera of patients with a range of other rheumatic diseases including scleroderma, Gougerot-Sjögren's syndrome, polymyositis / dermatomyositis, systemic sclerosis, and rheumatoid arthritis².

The snRNPs are a group of nuclear particles comprised of several polypeptides associated with a small nuclear RNA molecule. The snRNPs make up the spliceosome, responsible for splicing precursor mRNA into mature mRNA^3,4. Whereas autoantibodies directed against Sm are able to react with a wide range of snRNAs, RNP autoantibodies are only able to react with one particular type, referred to as U1snRNA.

Anti-RNP antibodies react with the U1 snRNP-specific polypeptides (68K, A and C antigens) whereas anti-Sm antibodies react with polypeptides associated with U1 snRNP-specific polypeptides, plus U2, U5 and U4/U6 snRNAs (B,B', D, E, F and G antigens)4. While the 68K polypeptide (also known RNP-70) constitutes the major MCTD RNP autoantigen, the major Sm autoantigen is represented by the D polypeptide^5,6.

Human RNP and Sm antigen sequences have a very high homology to bovine antigens, and calf thymus has long been used to detect the snRNP antigens in patient sera⁴. The RNP-68K (present as a 33/35K doublet on SDS-PAGE) and Sm, 19kDa to 10kDa polypeptides, represent the most abundant components of AROTEC's RNP-Sm antigen. Other snRNP subunits (RNP-A, RNP-C) are also detectable. The antigen typically exhibits a 260nm/280nm absorbance ratio of >1.3, suggesting that a significant snRNA component is present.