[Cloning and analysis of genetic determinants determining the production of microcin B2 and B27]

Cloning of plasmid genes for the synthesis of two peptide broad-spectrum antibiotics-microcins B2 and B27- and for host cell immunity to their action was performed. Recombinant plasmids containing these genes were designated pBE108 and pVB27, respectively. Deletional derivatives of plasmid pBE108 and mutant plasmids were obtained via transposon Tn5 insertions, which did not determine production of microcin B2 and immunity to it. Phenotypic study and physical mapping of these plasmids demonstrated that a 4.2-kb DNA fragment is responsible for B2 microcin production; immunity is provided by a 1.4-kb DNA fragment. A 5-kb DNA fragment is necessary for microcin B27 synthesis and expression of immunity to its action. Homology between these fragments and with plasmid DNA for the synthesis of microcin B17 and immunity to it was found. Homology between plasmid genes determining synthesis of type B and C microcins and host cell immunity to them was not observed. The production of B27 microcin is controlled by the product of the ompR gene; B2 microcin synthesis does not depend on this product. The mutations recA and lexA increase the susceptibility of Escherichia coli cells to the action of microcins B2 and B27 but not microcin C51.