Figure 3. Codon bias in high expression genes and conserved sites.

(a) There is a strong positive correlation between strength of codon bias in high expression genes, δ_H, and tRNA gene copy number. (b) There is no correlation between the strength of bias in conserved sites, δ_C, and tRNA gene copy number. The fact that δ_C is much smaller than δ_H suggests that selection for translational speed is more important than accuracy in these bacteria.