Aminoglycoside antibiotics promiscuously bind to structurally diverse RNA molecules containing internal bubbles and bulges with affinities in the microM range. An interesting exception is found in the human 12S mitochondrial decoding region where aminoglycoside binding, unlike in the case of its bacterial and human cytoplasmic counterparts, is absent. Mutations that reduce the size of the bubble in the 12S decoding region immediately restore aminoglycoside binding, giving the system chemical switch like behavior.