Evolution rates of genes on leading and lagging DNA strands

One of the main causes of bacterial chromosome asymmetry is replication-ass ociated mutational pressure. Different rates of nucleotide substitution acc umulation on leading and lagging strands implicate qualitative and quantita tive differences in the accumulation of mutations in protein coding sequenc es lying on different DNA strands. We show that the divergence rate of orth ologs situated on leading strands is lower than the divergence rate of thos e situated on lagging strands. The ratio of the mutation accumulation rate for sequences lying on lagging strands to that of sequences lying on leadin g strands is rather stable and time-independent. The divergence race of seq uences which changed their positions, with respect to the direction of repl ication fork movement, is not stable-sequences which have recently changed their positions are the most prone to mutation accumulation. This effect ma y influence estimations of evolutionary distances between species and the t opology of phylogenetic trees.