Opal terminator codon

Strauss, E. G., Rice, C. M., and Strauss, J. H., 1983, The sequence coding for the alphavirus nonstructural proteins is interrupted by an opal termination codon, Proc. Natl. Acad. Sci. USA 80 5271. 

Protein synthesis stops when a protein release factor (RF) recognizes specific termination signals contained in the RNA sequence. Three stop or nonsense codons have been identified UAG (amber), UAA (ochre), and UGA (opal). [All ciliated protozoa deviate from the universal genetic code by translating either one or two termination codons into Gin or Cys (13).] Chain termination involves the nucleophilic attack by water on the ester bond between the 3 -adenosine of tRNA and the amino acid. 

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