Chromosome partitioning at the initiation of sporulation in Bacillus subtilis

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The mechanism of chromosome partitioning at the initiation of sporulation in Bacillus subtilis is so far not much studied, but it is a very important subject concerning the cellular differentiation and chromosome replication. Sporulation initiation signals are sensed by the phosphorelay system and the sporulation is initiated by the accumulation of the response regulator spoOA-P.Several environ-mental signals, such as nutrient deprivation, DNA replication and partitioning, cell division, and cell density, are input into the phosphorelay system and regulate the concentration of the active SpoOA.The spoOJ operon (spoOJA-spoOJB) is located near the replication origin of the B.subtilis chromosome. It is a homology of the parA-parB operon which plays an important role in the plasmid partitioning. The roj, which encodes a SpoOJB homolog, is located upstream of the spoOJ operon.In the present study we have analyzed the function of these genes. We found that (i) spoOJB is necessary for the chromosome partitioning of the vegetative cells, (ii) SpoOJA protein represses the phosphorelay and the asymmetric septation or chromosome partitioning at the initiation of sporulation (stage I), and (iii) SpoOJB protein represses the function of SpoOJA ; i.e.SpoOJB participates in the chromosome partitioning at the initiation of sporulation through SpoOJA.The fact that the SpoOJA/SpoOJB repress the phosphorelay and chromsome partitioning suggests that SpoOJA/SpoOJB coordinate these mechanisms. We also analyzed the transcriptional regulation of the spoOJ operon and found that Roj protein is a repressor of the spoOJ operon and the expression of the spoOJ operon is repressed by SpoOA at the initiation of sporulation.