Abstract
The %(G + C) of bacterial genomes ranges from 25% in Mycoplasma to 75% in Micrococcus. Our model for horizontal gene flow enabled a theoretical study of the adaptation of relative codon frequency to match the pattern of the tRNA set of a new host. This study explored the dynamic relationship of %(G + C) to vectors of relative codon frequency (F γ ), relative amino acid coding frequency (F α ), and absolute codon frequency (F|γ|) in chromosomes of nine, fully sequenced bacterial genomes that varied widely in %(G + C). At constant F α , the theoretical maximum average range possible was %(G + C) = 37.4 ± 0.9%. In simulations of F γ adaptation to a new host following hypothetical gene transfer, we modeled %(G + C) as a function of F γ and F α . The simulation revealed that %(G + C) is dependent on F γ and F α in an explicit relationship described in this paper. We conclude that (1) F γ and F α determine %(G + C), and (2) the degree of adaptation of %(G + C) in a transferred gene depends upon the degree of F γ equilibration and the similarity of F α of the transferred gene to that of the new host.
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