Microcin B17 (McB17) is a 43 residue peptide antibiotic ribosomally synthesized in several strains of Escherichia coli. 1 Recently, we2 and others3 have reported that fourteen of these residues are posttranslationally modified; two Gly-Cys and Gly-Ser dipeptides lead, respectively, to two isolated thiazole and oxazole rings, whereas two tripeptides Gly-Cys-Ser and Gly-Ser-Cys produce two directly connected thiazole-oxazole ring systems. The ...
