The Structural Gene for Microcin H47 Encodes a Peptide Precursor with Antibiotic Activity

Microcin H47 is a bactericidal antibiotic produced by a naturally occurring Escherichia coli strain isolated in Uruguay. The microcin genetic system is located in the chromosome and extends over a 10-kb DNA segment containing the genes required for microcin synthesis, secretion, and immunity. The smallest microcin synthesis gene, mchB, was sequenced and shown to encode a highly hydrophobic peptide. An mchB-phoA gene fusion, which directed the synthesis of a hybrid bifunctional protein with both PhoA and microcin H47-like activities, was isolated. The results presented herein lead us to propose that microcin H47 is indeed a ribosomally synthesized peptide antibiotic and that its peptide precursor already has antibiotic activity of the same specificity as that of mature microcin.