['The acetamidase of Mycobacterium smegmatis is a highly inducible enzyme. Expression of this enzyme is increased 100-fold when the substrate acetamide is present. The acetamidase gene is found immediately downstream of three open reading frames. Two of these are proposed to be involved in regulation.', 'We constructed a deletion mutant in one of the upstream ORFs (amiA). This mutant (Mad1) showed a constitutively high level of acetamidase expression. We identified four promoters in the upstream region using a beta-galactosidase reporter gene. One of these (P2) was inducible in the wild-type, but was constitutively active in Mad1.'] Is amiA a negative regulator of acetamidase expression in Mycobacterium smegmatis?