Segment I

Segment I (shown in green) consists of five ORFs
comprising the composite resistance transposon
Tn5432. The insertion sequences IS1249b
(ORF1) and IS1249a (ORF5) flank the erythromycin
resistance gene region ermCX (ORF3) and
ermLP (ORF4). An identical copy of IS1249 occurs
in ORF29 (segment VIII). ORF3, the central
region of Tn5432, encodes a 23 S rRNA methyltransferase
preceded by a short leader peptide
probably involved in the regulation of erythromycin-
inducible translational attenuation.
This region is virtually identical to the antibiotic
resistance gene region (erythromycin, clindamycin)
of plasmid pNG2 from C. diphtheriae
S601.