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A Metazoan/Plant-like Capping Enzyme and Cap Modified Nucleotides in the Unicellular Eukaryote Trichomonas vaginalis

PLoS Pathogens, Jul 2010, Vol.6(7) [Peer Reviewed Journal]

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  • Title:
    A Metazoan/Plant-like Capping Enzyme and Cap Modified Nucleotides in the Unicellular Eukaryote Trichomonas vaginalis
  • Author: Simoes-Barbosa, Augusto ; Hirt, Robert ; Johnson, Patricia
  • Found In: PLoS Pathogens, Jul 2010, Vol.6(7) [Peer Reviewed Journal]
  • Subjects: Eukaryotes ; Ribonucleic Acid–RNA ; Evolution ; Polypeptides ; Fungi ; Phylogenetics ; Yeast
  • Language: English
  • Description: The cap structure of eukaryotic messenger RNAs is initially elaborated through three enzymatic reactions: hydrolysis of the 5'-triphosphate, transfer of guanosine through a 5'-5' triphosphate linkage and N7-methylation of the guanine cap. Three distinctive enzymes catalyze each reaction in various microbial eukaryotes, whereas the first two enzymes are fused into a single polypeptide in metazoans and plants. In addition to the guanosine cap, adjacent nucleotides are 2'-O-ribose methylated in metazoa and plants, but not in yeast. Analyses of various cap structures have suggested a linear phylogenetic trend of complexity. These findings have led to a model in which plants and metazoa evolved a two-component capping apparatus and modification of adjacent nucleotides while many microbial eukaryotes maintained the three-component system and did not develop modification of adjacent nucleotides. Here, we have characterized a bifunctional capping enzyme in the divergent microbial eukaryote Trichomonas vaginalis using biochemical and phylogenetic analyses. This unicellular parasite was found to harbor a metazoan/plant-like capping apparatus that is represented by a two-domain polypeptide containing a C-terminus guanylyltransferase and a cysteinyl phosphatase triphosphatase, distinct from its counterpart in other microbial eukaryotes. In addition, T. vaginalis mRNAs contain a cap 1 structure represented by m7GpppAmpUp or m7GpppCmpUp; a feature typical of metazoan and plant mRNAs but absent in yeast mRNAs. Phylogenetic and biochemical analyses of the origin of the T. vaginalis capping enzyme suggests a complex evolutionary model where differential gene loss and/or acquisition occurred in the development of the RNA capping apparatus and cap modified nucleotides during eukaryote diversification.
  • Identifier: DOI: 10.1371/journal.ppat.1000999

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