Analysis of 15 complete bacterial chromosomes revealed important biases in
gene organization. Strong compositional asymmetries between the genes lying
on the leading versus lagging strands were observed at the level of nucleo
tides, codons and, surprisingly, amino acids. For some species, the bias is
so high that the sole knowledge of a protein sequence allows one to predic
t with almost no errors whether the gene is transcribed from one strand or
the other. Furthermore, we show that these biases are not species specific
but appear to be universal. These findings may have important consequences
in our understanding of fundamental biological processes in bacteria, such
as replication fidelity, codon usage in genes and even amino acid usage in
proteins.