Evolution Rates of Genes on Leading and Lagging DNA Strands

One of the main causes of bacterial chro- mosome asymmetry is replication-associated mutational pressure. Different rates of nucleotide substitution accu- mulation on leading and lagging strands implicate quali- tative and quantitative differences in the accumulation of mutations in protein coding sequences lying on different DNA strands. We show that the divergence rate of or- thologs situated on leading strands is lower than the di- vergence rate of those situated on lagging strands. The ratio of the mutation accumulation rate for sequences lying on lagging strands to that of sequences lying on leading strands is rather stable and time-independent. The divergence rate of sequences which changed their positions, with respect to the direction of replication fork movement, is not stable—sequences which have recently changed their positions are the most prone to mutation accumulation. This effect may influence estimations of evolutionary distances between species and the topology of phylogenetic trees.