Genetic code 1990. Outlook.
The genetic code is evolving as shown by 9 departures from the universal code: 6 of them are in mitochondria and 3 are in nuclear codes. We propose that these changes are preceded by disappearance of a codon from coding sequences in mRNA of an organism or organelle. The function of the codon that disappears is taken by other, synonymous codons, so that there is no change in amino acid sequences of proteins. The deleted codon then reappears with a new function. Wobble pairing between anticodons and codons has evolved, starting with a single UNN anticodon pairing with 4 codons. Directional mutation pressure affects codon usage and may produce codon reassignments, especially of stop codons. Selenocysteine is coded by UGA, which is also a stop codon, and this anomaly is discussed. The outlook for discovery of more changes in the code is favorable, and open reading frames should be compared with actual sequential analyses of protein molecules in this search.
Jukes
T H
TH
Space Sciences Laboratory, University of California/Berkeley, Oakland 94608.
D000693:Anaerobiosis; D000926:Anticodon; D001483:Base Sequence; D005075:Biological Evolution; D003062:Codon; D003545:Cysteine / Q000031:analogs & derivatives / Q000378:metabolism; D004272:DNA, Mitochondrial / Q000235:genetics; D005560:Formate Dehydrogenases / Q000235:genetics; D005815:Genetic Code; D008969:Molecular Sequence Data; D009154:Mutation; D010443:Peptide Chain Termination, Translational; D014176:Protein Biosynthesis; D012323:RNA Processing, Post-Transcriptional; D012333:RNA, Messenger / Q000235:genetics; D012343:RNA, Transfer / Q000235:genetics; D012643:Selenium / Q000378:metabolism; D017279:Selenocysteine
D000926:Anticodon; D003062:Codon; D004272:DNA, Mitochondrial; D012333:RNA, Messenger; D017279:Selenocysteine; D012343:RNA, Transfer; D005560:Formate Dehydrogenases; D012643:Selenium; D003545:Cysteine