title: Sm core variation in spliceosomal small nuclear ribonucleoproteins from Trypanosoma brucei.
abstract: Messenger RNA processing in trypanosomes by cis and trans splicing requires spliceosomal small nuclear ribonucleoproteins (snRNPs) U1, U2, U4/U6, and U5, as well as the spliced leader (SL) RNP. As in other eukaryotes, these RNPs share a core structure of seven Sm polypeptides. Here, we report that the identity of the Sm protein constituents varies between spliceosomal snRNPs: specifically, two of the canonical Sm proteins, SmB and SmD3, are replaced in the U2 snRNP by two novel, U2 snRNP-specific Sm proteins, Sm15K and Sm16.5K. We present a model for the variant Sm core in the U2 snRNP, based on tandem affinity purification-tagging and in vitro protein-protein interaction assays. Using in vitro reconstitutions with canonical and U2-specific Sm cores, we show that the exchange of two Sm subunits determines discrimination between individual Sm sites. In sum, we have demonstrated that the heteroheptameric Sm core structure varies between spliceosomal snRNPs, and that modulation of the Sm core composition mediates the recognition of small nuclear RNA-specific Sm sites.
authors.affiliation: Institut für Biochemie, Justus-Liebig-Universität Giessen, Giessen, Germany.
authors.forename: Pingping
authors.initials: P
authors.lastname: Wang
authors.forename: Zsofia
authors.initials: Z
authors.lastname: Palfi
authors.forename: Christian
authors.initials: C
authors.lastname: Preusser
authors.forename: Stephan
authors.initials: S
authors.lastname: Lücke
authors.forename: William S
authors.initials: WS
authors.lastname: Lane
authors.forename: Christian
authors.initials: C
authors.lastname: Kambach
authors.forename: Albrecht
authors.initials: A
authors.lastname: Bindereif
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001324:Autoantigens / Q000737:chemistry / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D008954:Models, Biological; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011485:Protein Binding; D015800:Protozoan Proteins / Q000737:chemistry / Q000378:metabolism*; D012342:RNA, Small Nuclear / Q000737:chemistry / Q000235:genetics; D017413:Ribonucleoprotein, U2 Small Nuclear / Q000378:metabolism*; D017411:Ribonucleoproteins, Small Nuclear / Q000737:chemistry / Q000378:metabolism*; D016415:Sequence Alignment; D017381:Spliceosomes / Q000378:metabolism*; D013379:Substrate Specificity; D014346:Trypanosoma brucei brucei / Q000378:metabolism*; D055517:snRNP Core Proteins
chemical_list: D001324:Autoantigens; D015800:Protozoan Proteins; D012342:RNA, Small Nuclear; D017413:Ribonucleoprotein, U2 Small Nuclear; D017411:Ribonucleoproteins, Small Nuclear; D055517:snRNP Core Proteins