Figure 4. Mechanism of action of ethambutol (adapted from 84-88). EMB interacts with the EmbCAB proteins encoded by the embC, embA, and embB genes, leading to inactivation of arabinogalactan synthesis. Mutations in the embB locus cause alterations in EmbB, possibly leading to an altered target for EMB. Alternatively, hyperexpression of the EmbCAB proteins could lead to EMB resistance. Inlet box: Organization of the emb operon in Mycobacterium tuberculosis (MTB).