MODULAR STRUCTURE OF MICROCIN H47 AND COLICIN V

Sección Fisiología y Genética Bacterianas, Facultad de Ciencias, Iguá 4225, Montevideo 11.400, Uruguay

^* To whom correspondence should be addressed. Email: magela{at}fcien.edu.uy.

	Abstract

Microcins are gene-encoded peptide antibiotics produced by enterobacteria which act on strains of Gram negative bacteria. In this work, we concentrated on higher-molecular-mass microcins, i.e. those possessing 60 or more amino acids. They can be subdivided into unmodified and post-translationally modified peptides. In both cases, they exhibit conserved C-terminal sequences which appear to be characteristic of each subgroup. In the hypothesis that these sequences could correspond to domains, gene fusions between the activity genes for the unmodified microcin colicin V and the modified microcin H47 were constructed. These two microcins differ in their mode of synthesis, in their uptake, in their target and in their specific immunity. Through this experimental approach, chimeric peptides with exchanged C-terminal sequences were encoded. Cells carrying the fusions in different genetic contexts were then assayed for antibiotic production. Many of them produced antibiotic activities with recombinant properties: the toxicity of one microcin and the mode of uptake of the other. The results led to the identification of a modular structure of colicin V and of microcin H47, with the recognition of two domains in their peptide chains: a toxic N-terminal domain and an uptake C-terminal domain. This modular design would be shared by other microcins from each subgroup.