title: Novel RNA catalysts for the Michael reaction.
abstract: BACKGROUND
  In vitro selected ribozymes with nucleotide synthase, peptide and carbon-carbon bond forming activity provide insight into possible scenarios on how chemical transformations may have been catalyzed before protein enzymes had evolved. Metabolic pathways based on ribozymes may have existed at an early stage of evolution.
  
  
  RESULTS
  We have isolated a novel ribozyme that mediates Michael-adduct formation at a Michael-acceptor substrate, similar to the rate-limiting step of the mechanistic sequence of thymidylate synthase. The kinetic characterization of this catalyst revealed a rate enhancement by a factor of approximately 10(5). The ribozyme shows substrate specificity and can act as an intermolecular catalyst which transfers the Michael-donor substrate onto an external 20-mer RNA oligonucleotide containing the Michael-acceptor system.
  
  
  CONCLUSIONS
  The ribozyme described here is the first example of a catalytic RNA with Michael-adduct forming activity which represents a key mechanistic step in metabolic pathways and other biochemical reactions. Therefore, previously unforeseen RNA-evolution pathways can be considered, for example the formation of dTMP from dUMP. The substrate specificity of this ribozyme may also render it useful in organic syntheses.
authors.affiliation: Kekulé-Institut für Organische Chemie und Biochemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Germany.
authors.forename: G
authors.initials: G
authors.lastname: Sengle
authors.forename: A
authors.initials: A
authors.lastname: Eisenführ
authors.forename: P S
authors.initials: PS
authors.lastname: Arora
authors.forename: J S
authors.initials: JS
authors.lastname: Nowick
authors.forename: M
authors.initials: M
authors.lastname: Famulok
mesh_terms: D001483:Base Sequence / Q000235:genetics; D003001:Cloning, Molecular / Q000379:methods; D003856:Deoxyuracil Nucleotides / Q000737:chemistry / Q000378:metabolism; D019418:Evolution, Chemical; D015723:Gene Library; D007700:Kinetics; D008969:Molecular Sequence Data; D009841:Oligonucleotides / Q000737:chemistry / Q000378:metabolism; D016337:RNA, Catalytic / Q000737:chemistry* / Q000302:isolation & purification* / Q000378:metabolism*; D012641:Selection, Genetic; D013379:Substrate Specificity / Q000502:physiology; D013938:Thymidine Monophosphate / Q000737:chemistry / Q000378:metabolism; D013940:Thymidylate Synthase / Q000737:chemistry / Q000378:metabolism
chemical_list: D003856:Deoxyuracil Nucleotides; D009841:Oligonucleotides; D016337:RNA, Catalytic; C434423:ribozyme UV5; D013938:Thymidine Monophosphate; C007267:2'-deoxyuridylic acid; D013940:Thymidylate Synthase