[Principles of prokaryotic genome organization]

The peculiarities of bacterial chromosome organization are discussed, based mainly on the data on Escherichia coli. Highly important for bacterial genome organization is its division into two approx. equal half-genomes undergoing periodically "exchanges" of some kind displayed as continuous inversions including the oriC region of replication initiation. It is believed that short oligonucleotides are comprised in either of half-genomes. The former are predominantly oriented as direct repeats, which ensures the possibility of formation of tandem duplications consisting of identical genes--under conditions when selection for enhancing functions of corresponding genes takes place. Multiple tandem duplications capable of excision of plasmatic gene copies seem to initiate horizontal gene transfer in bacteria. Tandem gene duplications are probably being formed in the process of bacterial genetic recombination as well, when, as a result of non-equal crossing over, gene alleles derived from different strains are united into a tandem.