How does replication-associated mutational pressure influence amino acid composition of proteins?

We have performed detrended DNA walks on whole prokaryotic genomes, on nonc oding sequences and, separately, on each position in codons of coding seque nces. Our method enables us to distinguish between the mutational pressure associated with replication and the mutational pressure associated with tra nscription and other mechanisms that introduce asymmetry into prokaryotic c hromosomes. In many prokaryotic genomes, each component of mutational press ure affects coding sequences not only in silent positions but also in posit ions in which changes cause amino acid substitutions in coded proteins. Asy mmetry in the silent positions of codons differentiates the rate of transla tion of mRNA produced From leading and lagging strands. Asymmetry in the am ino acid composition of proteins resulting from replication-associated muta tional pressure also corresponds to leading and lagging roles of DNA strand s, whereas asymmetry connected with transcription and coding function corre sponds to the distance of genes from the origin or terminus of chromosome r eplication.