The assumption that the genetic code is used exclusively by all forms of life. This is true with a few exceptions. In yeast mitochondria, CUA codes for threonine instead of leucine; and in mammalian mitochondria, AUA codes for methionine instead of isoleucine, and codons AGA and AGG signal termination instead of coding for arginine. UGA codes for tryptophan instead of signaling termination in mitochondria from both sources. In four ciliates, Tetrahymean thermophila, Stylonychia lemnae, Paramecium primaurelia, and P. tetraurelia, UAA and UAG encode the amino acid glutamine rather than serving as termination codons. In Mycoplasma capricolum, as in mitochondria, UGA encodes tryptophan rather than serving as a termination codon. See Chronology, 1961, von Ehrenstein and Lipmann; 1979, Barrell et al.; 1985, Horowitz and Gorowsky, Yamao; genetic code.
Subjects: Genetics and Genomics.