Stability and asymmetric replication of the Bacillus subtilis 168 chromosome structure

Chromosomal DNAs from a number of strains derived from Bacillus subtilis 168 were digested with restriction endonucleases NotI or SfiI, and the locations of chromosomal alterations were compared with the recently constructed standard NotI-SfiI restriction map (M. Itaya and T. Tanaka, J. Mol. Biol. 220:631-648, 1991). In general, the chromosome structure of B. subtilis 168 was found to be stable, as expected from the genetic stability of this species. DNA alterations, typically deletions, are formed in three limited loci on the chromosome. One of these alterations was characterized as a spontaneous deletion formed between rrn operons, and another occurred as a result of prophage SP beta excision. I found that oriC and terC are not located on precisely opposite sides of the chromosome. Replication in the counter clockwise direction was 196 kb longer than replication in the clockwise direction. The characteristic of length difference is not changed by deletion formation.