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 mcjABCD necessary for produ ction of and immunity to the cyclic peptide antibiotic microcin J25 (MccJ25 ) has been sequenced. mcjA encodes the primary structure of MccJ25 as a pre cursor endowed with an N-terminal extension of 37 amino acids. The products of mcjB 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 ex porters, was found to be required for MccJ25 secretion, thus explaining its ability to confer immunity to MccJ25.