METALLOREGULATION IN BACILLUS-SUBTILIS - ISOLATION AND CHARACTERIZATION OF 2 GENES DIFFERENTIALLY REPRESSED BY METAL-IONS

We have cloned two metal-regulated genes (mrgA and mrgC) from Bacillus subtilis by using transposon Tn917-lacZ. Both were isolated as iron-r epressible gene fusions, but the metal specificity and sensitivity of gene repression are distinct. Transcription of mrgA-lacZ is induced at the end of logarithmic-phase growth in minimal medium, and this induc tion is prevented by excess manganese, iron, cobalt, or copper. Limita tion for metal ions is sufficient for mrgA-lacZ induction, since resus pension in medium lacking both manganese and iron rapidly induces tran scription. Transcription of mrgC-lacZ is also induced by iron deprivat ion but is not repressed by added manganese or other metal ions. Expre ssion of mrgC-lacZ and a 2,3-dihydroxybenzoic acid-based siderophore i s repressed in parallel by iron, and in both cases, only iron effects repression. We have cloned and sequenced the promoter and regulatory r egions of both mrgA and mrgC. Both genes are preceded by a predicted s igma(A)-dependent promoter element with overlapping sequences similar to the iron box consensus element for recognition by the Escherichia c oli ferric uptake regulator protein (Fur). Mutation of the putative ir on box for gene mrgC leads to partial derepression in iron-replete med ium.