title: Xenopus LSm proteins bind U8 snoRNA via an internal evolutionarily conserved octamer sequence.
abstract: U8 snoRNA plays a unique role in ribosome biogenesis: it is the only snoRNA essential for maturation of the large ribosomal subunit RNAs, 5.8S and 28S. To learn the mechanisms behind the in vivo role of U8 snoRNA, we have purified to near homogeneity and characterized a set of proteins responsible for the formation of a specific U8 RNA-binding complex. This 75-kDa complex is stable in the absence of added RNA and binds U8 with high specificity, requiring the conserved octamer sequence present in all U8 homologues. At least two proteins in this complex can be cross-linked directly to U8 RNA. We have identified the proteins as Xenopus homologues of the LSm (like Sm) proteins, which were previously reported to be involved in cytoplasmic degradation of mRNA and nuclear stabilization of U6 snRNA. We have identified LSm2, -3, -4, -6, -7, and -8 in our purified complex and found that this complex associates with U8 RNA in vivo. This purified complex can bind U6 snRNA in vitro but does not bind U3 or U14 snoRNA in vitro, demonstrating that the LSm complex specifically recognizes U8 RNA.
authors.affiliation: Genetics and Biochemistry Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892-1766, USA.
authors.forename: Nenad
authors.initials: N
authors.lastname: Tomasevic
authors.forename: Brenda A
authors.initials: BA
authors.lastname: Peculis
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D017124:Conserved Sequence; D003432:Cross-Linking Reagents / Q000737:chemistry; D019143:Evolution, Molecular; D005260:Female; D008969:Molecular Sequence Data; D063211:N-Terminal Acetyltransferase C; D009865:Oocytes; D012342:RNA, Small Nuclear / Q000737:chemistry / Q000378:metabolism*; D020537:RNA, Small Nucleolar / Q000737:chemistry / Q000378:metabolism*; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D017414:Ribonucleoprotein, U4-U6 Small Nuclear / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D017411:Ribonucleoproteins, Small Nuclear; D014981:Xenopus / Q000235:genetics*; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D003432:Cross-Linking Reagents; C485751:LSM4 protein, human; C485752:LSm4 protein, Xenopus; C117009:NAA38 protein, human; D012342:RNA, Small Nuclear; D020537:RNA, Small Nucleolar; D016601:RNA-Binding Proteins; D017414:Ribonucleoprotein, U4-U6 Small Nuclear; D017411:Ribonucleoproteins, Small Nuclear; D029867:Xenopus Proteins; D063211:N-Terminal Acetyltransferase C