Sequence and properties of mecA, a negative regulator of genetic competence in Bacillus subtilis

Abstract

The development of competence in Bacillus subtilis is regulated by growth conditions and several regulatory genes. In complex media competence development is poor, and there is little or no expression of late competence genes. mec mutations permit competence development and late competence gene expression in complex media, and bypass the requirements for many of the competence regulatory genes. In this paper we describe the cloning and characterization of mecA. The mecA gene product acts negatively in the development of competence. Null mutations in mecA allowed expression of a late competence gene comG, under conditions where it is not normally expressed, including in complex media and in cells mutant for several competence regulatory genes. Overexpression of MecA from a multicopy plasmid resulted in inhibition of comG transcription. The DNA sequence of mecA was determined and the predicted gene product showed no significant similarity to any protein in the database. Expression of a mecA-lacZ translational fusion was constitutive during growth and did not vary significantly in the different media tested. The role of mecA in competence development and other stationary phase phenomena is discussed.

The regulation of competence transcription factor synthesis constitutes a critical control point in the regulation of competence in Bacillus subtilis

“…The mutational inactivation of mecA increases the expression of late competence genes (10,28). In addition, overexpression of MecA results in a severe decrease in late competence gene expression (28).…”

“…The mutational inactivation of mecA increases the expression of late competence genes (10,28). In addition, overexpression of MecA results in a severe decrease in late competence gene expression (28). Since comK is a regulatory gene required for late competence gene expression (51,54), it was of interest to determine the effect of MecA deficiency on comK expression.…”

“…A second prediction is that null mutations in mecA will fail to bypass the need for ComK in late gene induction. A third is that MecA elimination and overproduction should cause the overexpression and inhibition, respectively, of ComK synthesis, similar to the demonstrated effects on comG, a representative late competence gene (28). These predictions have been tested, and the results are presented in this report.…”

“…The synthesis of the late gene products is negatively regulated by the products of mecA and mecB (10,27,28,35,44). It has been postulated that the Mec proteins serve to sequester or otherwise inactivate ComK (27,35).…”

A new Bacillus subtilis gene, med, encodes a positive regulator of comK

“…Although the enzymes for surfactin synthesis are not required for competence development (52), activation of the srfA operon by phosphorylated ComA results in the expression of comS, a gene embedded in the srfA operon (4,5,15). The small ComS peptide activates the competence transcription factor ComK by antagonizing the effects of MecA and ClpC (MecB), which inactivate ComK through protein-protein interactions (5,10,18,19,25,46). Another positive regulator of competence development, SinR, may be required for optimal comS expression (10,21).…”