ClpC regulates the fate of a sporulation initiation sigma factor, σH protein, in Bacillus subtilis at elevated temperatures

Abstract

Using a strain carrying a clpC–bgaB transcriptional fusion at the amyE locus, we found that the expression of a clpC operon was induced at the end of exponential growth in a σ^B-independent manner and ceased around T_3.5 in the wild type but not in a spo0H mutant. This suggests that some gene product(s) whose expression is dependent on σ^H function is required for the turn-off of clpC transcription during an early stage of sporulation. A clpC deletion mutant showed a temperature-sensitive sporulation phenotype and exhibited an abnormally large accumulation of σ^H in the cell at 45°C after T₂, at which time the σ^H level in the wild type had begun to decrease. These results, together with the fact that spo0H transcription in the clpC deletion mutant was similar to that of the wild type, suggested that ClpC may be responsible for the degradation of σ^H after the accomplishment of its role in sporulation. Moreover, as expected from these results, overproduction of Spo0A was also observed after the initiation of sporulation in the clpC deletion mutant at 45°C.