Genetic analysis of microcin H47 immunity.

Microcin H47 is a bactericidal antibiotic produced by a natural Escherichia coli isolate. The genetic system encoding microcin production and immunity consists of at least seven clustered genes. Four of these are devoted to microcin biosynthesis and two genes are required for its secretion into the extracellular medium. The product of the seventh gene, mchI, determines the cell's self-immunity. This gene was shown to encode a highly hydrophobic 69-residue peptide. Analysis of the MchI amino acid sequence, as well as the characterization of MchI-PhoA hybrid proteins, indicated that the microcin immunity product is probably exported out of the cytoplasm and remains an integral membrane peptide. This localization of the immunity peptide points to the cellular membrane as the site of action of microcin H47.