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The canonical pathway for selenocysteine insertion is dispensable in Trypanosomes

By Eric Aeby, Sotiria Palioura, Mascha Pusnik, Janine Marazzi, Allyson Lieberman, Elisabetta Ullu, Dieter Söll and André Schneider


The micronutrient selenium is found in proteins as selenocysteine (Sec), the 21st amino acid cotranslationally inserted in response to a UGA codon. In vitro studies in archaea and mouse showed that Sec-tRNASec formation is a 3-step process starting with serylation of tRNASec by seryl-tRNA synthetase (SerRS), phosphorylation of serine to form phosphoserine (Sep)-tRNASec by phosphoseryl-tRNASec kinase (PSTK), and conversion to Sec-tRNASec by Sep-tRNA:Sec-tRNA synthase (SepSecS). However, a complete study of eukaryotic selenoprotein synthesis has been lacking. Here, we present an analysis of Sec-tRNASec formation in the parasitic protozoon Trypanosoma brucei in vivo. Null mutants of either PSTK or SepSecS abolished selenoprotein synthesis, demonstrating the essentiality of both enzymes for Sec-tRNASec formation. Growth of the 2 knockout strains was not impaired; thus, unlike mammals, trypanosomes do not require selenoproteins for viability. Analysis of conditional RNAi strains showed that SerRS, selenophosphate synthase, and the Sec-specific elongation factor, EFSec, are also essential for selenoprotein synthesis. These results with T. brucei imply that eukaryotes have a single pathway of Sec-tRNASec synthesis that requires Sep-tRNASec as an intermediate

Topics: Biological Sciences
Publisher: National Academy of Sciences
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Provided by: PubMed Central
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