Selection pressures on codon usage in the complete genome of bacteriophage T7
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We searched the complete 39,936 base DNA sequence of bacteriophage T7 for nonrandomness that might be attributed to natural selection. Codon usage in the 50 genes of T7 is nonrandom, both over the whole code and among groups of synonymous codons. There is a great excess of purineany base-pyrimidine (RNY) codons. Codon usage varies between genes, but from the pooled data for the whole genome (12,145 codons) certain putative selective constraints can be identified. Codon usage appears to be influenced by host tRNA abundance (particularly in highly expressed genes), tRNA-mRNA interactions (one such interaction being perhaps responsible for maintaining the excess of RNY codons) and a lack of short palindromes. This last constraint is probably due to selection against host restriction enzyme recognition sites; this is the first report of an effect of this kind on codon usage. Selection against susceptibility to mutational damage does not appear to have been involved.
Key wordsBacteriophage T7 DNA sequence analysis Codon usage Molecular evolution Synonymous codons RNY codons Restriction sites tRNA Pretermination codons
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- Eigen M, Gardiner W, Schuster P, Winkler-Oswatitsch R (1981) The origin of genetic information. Sci Am 244(4):78–94Google Scholar
- Ikemura T (1982) Correlation between the abundance of yeast tRNAs and the occurrence of the respective codons in protein genes. Differences in synonymous codon choice patterns of yeast andEscherichia coli with reference to the abundance of isoaccepting transfer RNAs. J Mol Biol 158:573–598CrossRefPubMedGoogle Scholar
- Ikemura T, Ozeki H (1982) Codon usage and transfer RNA contents: organism-specific codon-choice patterns in reference to the isoacceptor contents. Cold Spring Harbor Symp Quant Biol 47:1087–1097Google Scholar
- Kimura M (1983) The neutral theory of molecular evolution. Cambridge University Press, CambridgeGoogle Scholar
- Van Valen L (1973) A new evolutionary law. Evol Theory 1: 1–30Google Scholar