The nonrandom use of synonymous codons. Such biases have been observed in genes from both prokaryotes and eukaryotes. For example, 90% of the leucines in the outer membrane protein of E. coli are encoded by one of the six synonymous leucine codons. There seems to be a positive correlation between the relative frequencies of the synonymous codons in the genes of a given species and the relative abundances of their cognate tRNAs. So codon usage may be determined by translational efficiency. See genetic code, transfer RNA.
Subjects: Genetics and Genomics.