FIG. 4.

Frequent mutations causing loss or gain of vanK function in Acinetobacter. The gene acquired a homopolymeric G tract during its evolutionary divergence from related transporters. Evidently slippage during replication can cause loss of a G residue from the tract. This mutation introduces a stop codon directly downstream from the G tract. The deletion reverts readily, so most populations of the Acinetobacter cell line have a mixture of wild-type cells and cells containing the deletion mutation.