Sequence Analysis of the Four Plasmid Genes Required To Produce the Circular Peptide Antibiotic Microcin J25

A 4.8-kb plasmid region carrying the four genes mcjABCDnecessary for production of and immunity to the cyclic peptide antibiotic microcin J25 (MccJ25) has been sequenced. mcjAencodes the primary structure of MccJ25 as a precursor endowed with an N-terminal extension of 37 amino acids. The products ofmcjB and mcjC are thought to be involved in microcin maturation, which implies cleavage of McjA and head-tail linkage of the 21-residue pro-MccJ25. The predicted McjD polypeptide, which is highly similar to several ABC exporters, was found to be required for MccJ25 secretion, thus explaining its ability to confer immunity to MccJ25.