CLPC REGULATES THE FATE OF A SPORULATION INITIATION SIGMA-FACTOR, SIGMA(H) PROTEIN, IN BACILLUS-SUBTILIS AT ELEVATED-TEMPERATURES

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 t he end of exponential growth in a sigma(B)-independent manner and ceas ed around T-3.5 in the wild type but not in a spoOH mutant. This sugge sts that some gene product(s) whose expression is dependent an sigma(H ) function is required for the turn-off of clpC transcription during a n early stage of sporulation. A clpC deletion mutant showed a temperat ure-sensitive sporulation phenotype and exhibited an abnormally large accumulation of sigma(H) in the cell at 45 degrees C after T-2, at whi ch time the sigma(H) level in the wild type had begun to decrease. The se results, together with the fact that spoOH transcription in the clp C deletion mutant was similar to that of the wild type, suggested that ClpC may be responsible far the degradation of sigma(H) after the acc omplishment of its role in sporulation. Moreover, as expected from the se results, overproduction of SpoOA was also observed after the initia tion of sporulation in the clpC deletion mutant at 45 degrees C.