The role of Spo0j in Bacillus subtilis sporulation involves the phosphorelay pathway

The Bacillus subtilis spo0J gene is involved in chromosome partitioning and the initiation of sporulation. spo0J lies in an operon that also contains soj. soj encodes a protein that may inhibit activation of transcription by Spo0A. Using spo::lacZ fusions, we examined spo0J as a target of regulation and a regulator of gene expression. Activity from the soj-spo0J promoter was elevated in a spo0B mutant, suggesting that soj-spo0J expression may be controlled by Spo0B, a phosphotransferase that transports phosphate from Spo0F to Spo0A in the phosphorelay pathway controlling the initiation of sporulation. In particular, Spo0B may phosphorylate a repressor of the soj-spo0J operon, thereby downregulating soj-spo0J expression. Studies examining spo0J as a regulator revealed that spoIIA and spoIIG expression was not induced in a spo0J mutant. Double mutants carrying an additional mutation in soj exhibited intermediate levels of spoIIG expression. spoIIJG levels in soj single mutants were also intermediate relative to wild-type cells and spo0J mutants, suggesting that both soj and spo0J are necessary for maximal expression. spoIIA and spoIIG encode sigma factors involved in early sporulation. Since spoIIA and spoIIG expression is activated by Spo0A binding, a spo0J mutation may downregulate their expression through Spo0A via Soj. Excess Soj may decrease expression from Spo0A promoters while the Soj-Spo0J complex may enhance expression from Spo0A promoters. Supporting this hypothesis, a spo0J mutation lowered sinR expression approximately 2.5 hrs into stationary phase. sinR, which encodes a DNA binding protein, is also activated by Spo0A during sporulation. Since ftsA and ftsZ encode cell division proteins, the effect of spo0J on ftsAZ expression was also examined. A spo0J mutation was correlated with increased ftsAZ expression approximately 4 hrs into stationary phase, suggesting that spo0J may affect chromosome partitioning through ftsAZ