A NEW BACILLUS-SUBTILIS GENE, MED, ENCODES A POSITIVE REGULATOR OF COMK

Bacillus subtilis degR, a positive regulator of the production of degr adative enzymes, is negatively regulated by the competence transcripti on factor ComK which is overproduced in mecA null mutants. We used tra nsposon Tn10 to search for a mutation that reduced the repression leve l of degR caused by a mecA mutation. A new gene exerting positive regu lation on comK was obtained and designated med (suppressor of mecA eff ect on degR). Sequence determination, Northern analysis, and primer ex tension analyses revealed that the med gene contained an open reading frame (ORF) composed of 317 codons and was transcribed into an approxi mately 1,250-nucleotide mRNA together with its short downstream gene. The expression of comK is positively regulated by factors such as ComK itself, ComS (SrfA)-MecA, DegU, SinR, and AbrB. Quantitative analyses using comK'-'lacZ, srfA-lacZ, degU'-'lacZ, and sinR'-'lacZ fusions sh owed that disruption of med caused a significant decrease in comK expr ession in both mecA(+) and mecA strains, while expression of srfA, sin R, and degU was not affected by the mutation. An epistatic analysis re vealed that overproduction of ComK resulted in alteration of med expre ssion, suggesting a regulatory loop between comK and med. Several poss ible mechanisms for positive regulation of comK by Med are discussed.