Identification of a methylase gene for erythromycin resistance within the sequence of a spontaneously deleting fragment of Corynebacterium diphtheriae plasmid pNG2

A 9.6 Mda Corynebacterium diphtheriae plasmid, pNG2, mediates inducible resistance to erythromycin and other macrolide‐lincosamide‐streptogramin B (MLS) antibiotics. Spontaneous deletion of a 1.2 Mda fragment of pNG2 leaves the derivative plasmid incapable of conferring MLS‐resistance on its host. The pNG2 region containing this fragment was sequenced as were the regions flanking it. The fragment contained 1606 bp, was flanked by almost perfect 23 bp inverted repeats, and appeared to be excised precisely. It contained an open reading frame encoding a leader protein plus a protein which was similar in its amino acid sequence to the rRNA methylases produced by other erythromycin‐resistant, Gram‐positive bacteria. The C. diphtheriae gene was named ermCd.