BACKGROUND: Chromosomal DNA replication in bacteria starts at the origin (ori) 
and the two replicores propagate in opposite directions up to the terminus (ter) 
region. We hypothesize that the two replicores need to reach ter at the same 
time to maintain a physical balance; DNA insertion would disrupt such a balance, 
requiring chromosomal rearrangements to restore the balance. To test this 
hypothesis, we needed to demonstrate that ori and ter are in a physical balance 
in bacterial chromosomes. Using wavelet analysis, we documented GC skew, AT 
skew, purine excess and keto excess on the published bacterial genomic sequences 
to locate the turning (minimum and maximum) points on the curves. Previously, 
the minimum point had been supposed to correlate with ori and the maximum to 
correlate with ter.
RESULTS: We observed a strong tendency of the bacterial chromosomes towards a 
physical balance, with the minima and maxima corresponding to the known or 
putative ori and ter and being about half chromosome separated in most of the 
bacteria studied. A nonparametric method based on wavelet transformation was 
employed to perform significance tests for the predicted loci.
CONCLUSIONS: The wavelet approach can reliably predict the ori and ter regions 
and the bacterial chromosomes have a strong tendency towards a physical balance 
between ori and ter.