title: The human hnRNP M proteins: identification of a methionine/arginine-rich repeat motif in ribonucleoproteins.
abstract: Recent reports indicate that proteins which directly bind to nascent RNA polymerase II transcripts, the heterogeneous nuclear ribonucleoproteins (hnRNPs), play an important role in both transcript-specific packaging and alternative splicing of pre-mRNAs. Here we describe the isolation and characterization of a group of abundant hnRNPs, the M1-M4 proteins, which appear as a cluster of four proteins of 64,000-68,000 daltons by two-dimensional electrophoresis. The M proteins are pre-mRNA binding proteins in vivo, and they bind avidly to poly(G) and poly(U) RNA homopolymers in vitro. Covalently associated polyadenylated RNA-protein complexes, generated by irradiating living HeLa cells with UV light, were purified and used to elicit antibodies in mice. The resulting antisera were then employed to isolate cDNA clones for the largest M protein, M4, by immunological screening. The deduced amino acid sequence of M4 indicates that the M proteins are members of the ribonucleoprotein consensus sequence family of RNA-binding proteins with greatest similarity to a hypothetical RNA-binding protein from Saccharomyces cerevisiae. The M proteins also possess an unusual hexapeptide-repeat region rich in methionine and arginine residues (MR repeat motif) that resembles a repeat in the 64,000 dalton subunit of cleavage stimulation factor, which is involved in 3'-end maturation of pre-mRNAs. Proteins immunologically related to M exist in divergent eukaryotes ranging from human to yeast.
authors.affiliation: Department of Immunology and Medical Microbiology, College of Medicine, University of Florida, Gainesville 32610-0266.
authors.forename: K V
authors.initials: KV
authors.lastname: Datar
authors.forename: G
authors.initials: G
authors.lastname: Dreyfuss
authors.forename: M S
authors.initials: MS
authors.lastname: Swanson
mesh_terms: D016475:3T3 Cells; D000595:Amino Acid Sequence; D000818:Animals; D000911:Antibodies, Monoclonal; D001120:Arginine / Q000032:analysis*; D001483:Base Sequence; D002460:Cell Line; D004247:DNA; D006367:HeLa Cells; D034761:Heterogeneous-Nuclear Ribonucleoprotein Group M; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D006801:Humans; D015151:Immunoblotting; D008715:Methionine / Q000032:analysis*; D051379:Mice; D008969:Molecular Sequence Data; D012332:RNA, Heterogeneous Nuclear / Q000737:chemistry / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000378:metabolism*; D011817:Rabbits; D012091:Repetitive Sequences, Nucleic Acid; D012261:Ribonucleoproteins / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid
chemical_list: D000911:Antibodies, Monoclonal; D034761:Heterogeneous-Nuclear Ribonucleoprotein Group M; D034441:Heterogeneous-Nuclear Ribonucleoproteins; D012332:RNA, Heterogeneous Nuclear; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D004247:DNA; D001120:Arginine; D008715:Methionine