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

Antibodies to 5 M urea soluble chromosomal proteins from HeLa cells

The tissue specificity of a chromosomal protein fraction, extractable from chromatin with 5 M urea at low ionic strength, has been examined in HeLa, A549 and HT 29 cells. Electrophoresis in polyacrylamide gels indicates that each cell type has a different content of 5 M urea soluble proteins which are distinguishable from the histones, from the tight DNA-binding proteins and from the high-mobility-group chromosomal proteins. Antibodies against 5 M urea soluble proteins extracted from HeLa cells were produced in mice. Although each of the mice tested prior to immunization contained a detectable amount of antibodies against both the 5 M urea soluble proteins and tight DNA-binding proteins, immunization elevated the level of the antibodies in the serum over 100-fold. The antibodies do not distinguish between the 5 M urea extracts obtained from different sources because most of the antibodies are directed against antigens shared by the cells studied. Immunofluorescence studies reveal that components which cross-react with 5 M urea soluble chromosomal proteins are also present in the cytoplasm. We conclude the following. (1) 5 M urea extracts from chromatin a group of proteins which differs among cells. (2) Mice contain detectable amounts of autoantibodies against these chromosomal proteins. (3) Immunization with the 5 M urea extractable fraction elicits antibodies against a restricted number of antigenic components which are shared among the cells studied. (4) 5 M urea extractable proteins are found both in the nucleus and cytoplasm; part of these may be cytoskeletal elements. Because the antisera do not react with histones, high-mobility-group proteins and tight DNA-binding proteins, they may be used for various functional studies on the 5 M urea extractable chromosomal protein fraction.

Purification of snRNPs U1, U2, U4, U5 and U6 with 2,2,7-trimethylguanosine-specific antibody and definition of their constituent proteins reacting with anti-Sm and anti-(U1)RNP antisera

Small nuclear ribonucleoprotein particles (snRNPs) of the U-snRNP class from Ehrlich ascites tumor cells were purified in a one-step procedure by affinity chromatography with antibodies specific for 2,2,7-trimethylguanosine (m23.2.7G), which is part of the 5'-terminal cap structure of snRNAs U1-U5. Antibody-bound snRNPs are desorbed from the affinity column by elution with excess nucleoside m23.2.7G; this guarantees maintenance of their native structure. The snRNPs U1, U2, U4, U5 and U6 can be recovered quantitatively from nuclear extracts by this procedure. Co-isolation of U6 snRNP must be due to interactions between this and other snRNPs, as anti-m23.2.7G antibodies do not react with deproteinized U6 snRNA. We have so far defined nine proteins of approximate mol. wts. 10 000, 12 000, 13 000, 16 000, 21 000, 28 000, 32 000, 34 000 and 75 000. Purified snRNPs react with anti-(U1)RNP and with anti-Sm antisera from patients with mixed connective tissue disease and from MRL/l mice. As determined by the protein blotting technique, six of the snRNP polypeptides, characterized by apparent mol. wts. 13 000, 16 000, 21 000, 28 000, 34 000 and 75 000, bear antigenic determinants for one or the other of the above autoantibody classes. This suggests strongly that the U-snRNPs produced by the procedure described here are indeed representative of the snRNPs in the cell. With highly purified snRNPs available, investigation of possible enzymic functions of the particles may now be undertaken.

An assessment of the evidence for the role of ribonucleoprotein particles in the maturation of eukaryote mRNA

This article has sought to draw together, on the one hand, what is known of mRNA processing and its control and, on the other hand, what is known of the structure and validity of hnRNP and snRNP particles. At the same time, it has attempted to synthesize these two themes into a critical assessment of the evidence which suggests that the particles are intimately involved in processing. It cannot be said that the case is proven. The evidence is compelling but circumstantial. The last few years have seen the development of the first in vitro splicing systems (Weingartner and Keller, 1981; Goldenberg and Raskus, 1981; Kole and Weissman, 1982), the isolation of monoclonal antibodies to defined snRNP (Lerner et al., 1981a; Billings et al., 1982) and hnRNP proteins (Hugle et al., 1982), and the ability to use artificial lipid vesicles to transfer antisera (Lenk et al., 1982) and radioactive snRNA (Gross and Cetron, 1982) into cells. It is to be hoped that further refinements of these and other techniques will allow us to solve this, one of the major outstanding problems of molecular biology.