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Protein Eng. 1988 Sep;2(3):239-46.

Selenocysteine's mechanism of incorporation and evolution revealed in cDNAs of three glutathione peroxidases.

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Chiron Research Laboratories, Chiron Corporation, Emeryville, CA 94608.


The nonsense codon, UGA, has for the first time recently been shown to encode selenocysteine in two proteins, mouse glutathione peroxidase (GSH-Px) (EC and bacterial formate dehydrogenase. A co-translational rather than post-translational selenium-incorporation mechanism has been implicated. Furthermore, high expression levels of GSH-Px have suggested that suppression of termination is efficient and specific. We have isolated and characterized pituitary, kidney and placenta cDNAs for bovine, human and mouse GSH-Px respectively. It is demonstrated that this novel suppression event occurs in diverse tissues, in at least three mammalian species and at the translational step. Surprisingly, GSH-Px is shown to be extramitochondrially encoded, indicating a cytosolic suppression event rather than one utilizing the mitochondria's well-documented extended codon-reading ability. Sequence analysis reveals that a simple proximal contextual pattern responsible for readthrough does not exist. Analysis of predicted secondary structures of mRNAs, however, has revealed a conformation which may be unique to selenocysteine proteins and may prove useful as a tool for artificial incorporation of selenocysteines. A human intron for GSH-Px from an unspliced mRNA has been isolated whose position indicates an ancient, divergent evolutionary relationship with thioredoxin-S2, rather than an independent convergent one.

[Indexed for MEDLINE]

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