Replication generates bacterial chromosomes with strands that differ in the 
number of genes and base composition. It has been suggested that in bacteria 
such as Bacillus subtilis, PolC is responsible for the synthesis of the leading 
strand and DnaE for the lagging strand, whereas in many other bacteria DnaE is 
responsible for the synthesis of both strands. Here, I show that the possession 
of PolC correlates with leading strands that contain an average of 78% of genes 
compared with 58% for genomes that do not contain PolC. This suggests that 
asymmetrical replication forks could have a major role in defining and 
constraining the structure of the bacterial chromosome. The presence of PolC is 
not correlated with compositional strand bias, suggesting that the two biases 
result from different types of structural asymmetry.