Highly purified snRNPs retain antigenic determinants towards anti Sm antibodies

snRNPs purified by centrifugation in density gradients (BRUNEL et al. Nucl. Acids. Res., 1981, 9, 815–830 and SRI-WIDADA et al. Biochim. Biophys. Res. Commun., 1982, 104 , 457–462) retain an important part (46%) of their antigenicity towards anti-Sm antibodies indicating that antigenic determinants are among the small 4–5 polypeptides between 9 and 14,000 daltons found to be tightly associated with snRNAs. Furthermore, digestion of a great part of the RNA moiety does not abolish this antigenicity. As to the determinant for RNP antigen, our results suggest that it could depend on the three other proteins which are lost during the purification.