Asymmetric directional mutation pressures in bacteria

When there are no strand-specific biases in mutation and selection rates between the two strands of DNA, the average nucleotide composition is theoretically expected to be A = T and G = C within each strand. By focusing on weakly selected regions that could be oriented with respect to replication in 43 out of 51 completely sequenced bacterial chromosomes, asymmetric directional mutation pressures have been detected.