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Facile Recoding of Selenocysteine in Nature

  • Author(s): Mukai, T
  • Englert, M
  • Tripp, HJ
  • Miller, C
  • Ivanova, NN
  • Rubin, EM
  • Kyrpides, NC
  • Söll, D
  • et al.
Abstract

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Selenocysteine (Sec or U) is encoded by UGA, a stop codon reassigned by a Sec-specific elongation factor and a distinctive RNA structure. To discover possible code variations in extant organisms we analyzed 6.4 trillion base pairs of metagenomic sequences and 24 903 microbial genomes for tRNASecspecies. As expected, UGA is the predominant Sec codon in use. We also found tRNASecspecies that recognize the stop codons UAG and UAA, and ten sense codons. Selenoprotein synthesis programmed by UAG in Geodermatophilus and Blastococcus, and by the Cys codon UGU in Aeromonas salmonicida was confirmed by metabolic labeling with75Se or mass spectrometry. Other tRNASecspecies with different anticodons enabled E. coli to synthesize active formate dehydrogenase H, a selenoenzyme. This illustrates the ease by which the genetic code may evolve new coding schemes, possibly aiding organisms to adapt to changing environments, and show the genetic code is much more flexible than previously thought. Stop making sense: Selenocysteine is encoded by UGA, a stop codon reassigned by a Sec-specific elongation factor and a distinctive RNA structure. Analysis of 6.4 trillion base pairs of metagenomic sequences and about 25 000 genomes revealed tRNASecspecies that recognize the stop codons UAG and UAA, and ten sense codons. Thus the genetic code is much more flexible than previously thought.

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