amiA is a negative regulator of acetamidase expression in Mycobacterium smegmatis
1 Department of Medical Microbiology, Barts and the London, Queen Mary's School of Medicine and Dentistry, London, UK
2 Department of Infectious & Tropical Diseases, London School of Hygiene & Tropical Medicine, London, UK
BMC Microbiology 2001, 1:19 doi:10.1186/1471-2180-1-19Published: 31 August 2001
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 β-galactosidase reporter gene. One of these (P2) was inducible in the wild-type, but was constitutively active in Mad1.
These results demonstrate that amiA encodes a negative regulatory protein which interacts with P2. Since amiA has homology to DNA-binding proteins, it is likely that it exerts the regulatory effect by binding to the promoter to prevent transcription.