Segment II

Segment II (ORFs 6–14), located downstream of
Tn5432, contains the tetracycline resistance
genes tetA (ORF6) and tetB (ORF7). This segment
(ORFs 6–14) is very similar to ATP-binding cassette
(ABC) transporters identified in a mycobacterium
(M. smegmatis) chromosome. The
tandemly arranged genes tetA and tetB also mediate
resistance to the !-lactam antibiotic oxacillin,
although it is structurally and functionally
unrelated to tetracycline. Presumably this
results from TetAB protein heterodimerization
and subsequent export of the antibiotics out of
the bacterial cell. Similarly, the other segments
have been delineated.