Autoantibodies against small nuclear ribonucleoprotein components

Sera from patients with systemic rheumatic diseases often contain antibodies against nuclear antigens. Among these are proteins complexed with the small nuclear RNA (snRNA) U1, U2, U4, U5 and U6. In human cells, at least 11 different polypeptides (called 70K, A, A', B', B", B, C, D, E, F and G) ranging in molecular weight from 70 to 11 kDa, are associated with the snRNA, constituting the snRNP particles. In this report characteristics of 3 classes of autoantibodies are described. Anti-(U1) RNP antibodies recognize the U1 specific 70K and/or A and/or C proteins. Anti-Sm antibodies recognize proteins associated with all U snRNA, primarily the B', B and D proteins. Anti-(U1,U2) RNP sera contain antibodies directed against the U2 specific A' or B" proteins. These antibodies are useful tools for studying the structure and function of U snRNP complexes. Using mutant U2 snRNA and monospecific antibodies directed against the U2 specific proteins, we analyzed the interactions between proteins and RNA in the U2 snRNP particle. We have also isolated recombinant clones containing cDNA of mRNA coding for a number of snRNA associated proteins. Possible directions of future research are discussed.