MECB OF BACILLUS-SUBTILIS, A MEMBER OF THE CLPC ATPASE FAMILY, IS A PLEIOTROPIC REGULATOR CONTROLLING COMPETENCE GENE-EXPRESSION AND GROWTHAT HIGH-TEMPERATURE

The Bacillus subtilis DegS-DegU histidine kinase-response regulator pa ir controls the expression of genes encoding degradative enzymes such as levansucrase (sacB) and of genes involved in genetic competence. Th e mecA and mecB mutations were previously isolated as allowing compete nce gene expression in complex media. We have shown that the mec mutat ions also lead to overexpression of sacB, bypassing the DegS-DegU requ irement. This expression was shown to be entirely dependent upon ComK, a positive regulator of competence gene expression, The mecB gene was cloned and its nucleotide sequence was determined. The predicted MecB protein shows very high similarity over its entire length with member s of the CLpC family of ATPases (60% identity). MecB is essential for growth of B. subtilis at high temperature. MecB also acts as a negativ e regulator of ComK synthesis, thus preventing late competence gene ex pression, We suggest that under these conditions MecB may interact wit h MecA to sequester or otherwise inactivate ComK. In response to an un known signal, active ComK would accumulate through a positive feedback loop, leading to expression of competence genes allowing DNA uptake.