Substitution of selenocysteine for cysteine in a reticulocyte lysate protein synthesis system

Eric C. Wilhelmsen, Wayne C. Hawkes, Al L. Tappel

Research output: Contribution to journalArticlepeer-review

5 Scopus citations


Selenocysteine occurs in the peptide backbone of several selenoenzymes. The mechanism, of selenocysteine incorporation has not been well characterized. The incorporation of selenocysteine into protein in a rabbit reticulocyte lysate (RRL) was studied at high levels of selenocysteine. [75Se]Selenocysteine incorporation was inhibited by cycloheximide and by nuclease treatment. Random RNA copolymers were tested for protein synthesis activity in the messenger RNA-dependent RRL system. Of the active polymers, poly CIU and GU most strongly stimulated the incorporation of selenocysteine. In a series of four polymers with different ratios of U to G, incorporation of selenocysteine and cysteine increased with increasing percentages of U, suggesting that selenocysteine and cysteine responded to the same codon, presumably UGU. Of the 20 protein amino acids, only cysteine and cystine competed with selenocysteine incorporation. Selenocysteine was charged to cysteine-accepting tRNA in RRL. These results show that at supraphysiological concentrations selenocysteine can substitute for cysteine in RRL protein synthesis. Misincorporation of selenocysteine could be important when animal tissues contain high levels of selenium.

Original languageEnglish (US)
Pages (from-to)141-151
Number of pages11
JournalBiological Trace Element Research
Issue number3
StatePublished - Apr 1985


  • cysteine, substitution by selenocysteine
  • protein synthesis system, selenocysteine incorporation in a reticulocyte lysate
  • reticulocyte lysate, selenocysteine incorporation into protein in
  • Selenium, and protein synthesis
  • selenocysteine, specificity of incorporation
  • selenoproteins, synthesis of

ASJC Scopus subject areas

  • Endocrinology, Diabetes and Metabolism
  • Endocrinology
  • Biochemistry, Genetics and Molecular Biology(all)
  • Biochemistry, medical
  • Inorganic Chemistry
  • Clinical Biochemistry
  • Biochemistry


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