USE OF ASYMMETRIC CELL-DIVISION AND SPOIIIE MUTANTS TO PROBE CHROMOSOME ORIENTATION AND ORGANIZATION IN BACILLUS-SUBTILIS

Soon after the onset of sporulation in Bacillus subtilis, asymmetric c ell division occurs to generate the differentiating prespore and mothe r cell types. Formation of the septum close to the cell pole initially bisects the nucleoid destined for the prespore, trapping only about o ne-third of the DNA in the small compartment. The remaining part of th e chromosome is then transported through the septum, spoIIIE mutant ce lls fail to transfer the DNA and arrest with only partially segregated prespore chromosomes. Previous work has shown that the orientation of the chromesome at the time of septation is not random. Here, we use b oth physical and genetic methods to characterize the trapped DNA. The results show that the chromosome has a very specific orientation at th e time of septation, consistent with the action of a centromere-like s equence near oriC. They also demonstrate that the chromosome is folded , or otherwise organized, in a highly ordered manner.