ABSTRACT
Selenium was initially shown to exist in glutathione peroxidase and the selenium containing amino acid in protein was subsequently identified as selenocysteine. Selenocysteine has been shown to occur in a variety of proteins from a large number of organisms. The corresponding selenocysteyl- transfer ribonucleic acid (tRNA) and/or selenocysteyl-tRNA gene is known to be widespread, if not ubiquitous, in nature suggesting that selenocysteine belongs in the universal genetic code. The gene for selenocysteine tRNA has been shown to occur in single copy in the genomes of several mammals, including humans, rabbits, and cattle, and also in the genomes of chickens, Xenopus, Drosophila, and C. elegans. The selenocysteine tRNA gene was found to be widespread in the subkingdom, Eubacteria, and the selenocysteine tRNA gene and/or its gene product were found to be ubiquitous in the animal kingdom.
