A structural gene of heptapeptide, which is a component of the microcin C51 molecule, was identified by hybridization of plasmid DNA fragments and a mixture of synthesized oligonucleotides with the sequence corresponding to that of amino acids in the peptide. Sequence analysis of the structural gene of microcin peptide and its promoter region was performed. The data obtained indicate that the peptide of microcin C51 is synthesized on ribosomes. Four polypeptides of 67, 39, 16, and 14 kDa were identified using the system of minicells. These polypeptides are specified by a DNA fragment responsible for microcin synthesis and immunity in a producer cell. Apparently, three of these polypeptides with molecular masses of 67, 39, and 16 kDa are responsible for microcin production and immunity. The 67 kDa polypeptide is involved in the expression of immunity to microcin and, probably, in microcin production.