Selenocysteine, a highly specific component of certain enzymes, is incorporated by a UGA-directed co-translational mechanism.
The opal termination codon UGA is used in both prokaryotic and eukaryotic species to direct the specific insertion of selenocysteine into certain selenium-dependent enzymes. So far a formate dehydrogenase (hydrogenase-linked) of Escherichia coli and glutathione peroxidases of murine, human and rat origin have been identified as enzymes containing selenocysteine residues encoded by UGA. A novel seryl-tRNA, anticodon UCA, that specifically recognizes the UGA codon is required for selenocysteine incorporation into formate dehydrogenase. A eukaryotic UGA suppressor tRNA with UCA anticodon that accepts serine and is phosphorylated to O-phosphoseryl-tRNA may have a corresponding function in glutathione peroxidase synthesis. Other factors required for the unusual usage of the in-frame UGA codons to specify selenocysteine incorporation and the biochemical mechanism involved in distinguishing these from normal UGA termination codons are discussed.
Böck
A
A
Institut für Genetik und Mikrobiologie, Universität München, FRG.
Stadtman
T C
TC
D000594:Amino Acid Oxidoreductases / Q000096:biosynthesis; D000818:Animals; D003013:Clostridium / Q000201:enzymology; D003062:Codon; D003545:Cysteine / Q000031:analogs & derivatives* / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics; D005979:Glutathione Peroxidase / Q000096:biosynthesis; D009097:Multienzyme Complexes / Q000096:biosynthesis; D009154:Mutation; D010088:Oxidoreductases / Q000096:biosynthesis; D014176:Protein Biosynthesis; D012343:RNA, Transfer / Q000378:metabolism; D012643:Selenium / Q000378:metabolism*; D017279:Selenocysteine; D013728:Terminator Regions, Genetic
D003062:Codon; D009097:Multienzyme Complexes; D017279:Selenocysteine; D012343:RNA, Transfer; D010088:Oxidoreductases; D005979:Glutathione Peroxidase; D000594:Amino Acid Oxidoreductases; C020815:glycine reductase; D012643:Selenium; D003545:Cysteine