Читать книгу Snyder and Champness Molecular Genetics of Bacteria - Tina M. Henkin - Страница 205

Just because more than one codon can encode an amino acid does not mean that all the codons are used equally in all organisms. The same amino acid may be preferentially encoded by different codons in different organisms. This codon preference may reflect higher concentrations of certain tRNAs or may be related to the base composition of the DNA of the organism. While mammals have an average G+C content of about 50% (so that there are about as many AT base pairs in the DNA as there are GC base pairs), some bacteria and their viruses have very high or very low G+C contents. How the G+C content can influence codon preference is illustrated by some members of the genera Pseudomonas and Streptomyces. These organisms have G+C contents of almost 75%. To maintain such high G+C contents, the codon usage of these bacteria favors the codons that have the most G’s and C’s for each amino acid.