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amiA is a negative regulator of acetamidase expression in Mycobacterium smegmatis
T Parish1, J Turner, N G Stoker
1Department of Medical Microbiology, Barts and the London, Queen Mary's School of Medicine and Dentistry, London, UK. t.parish@mds.gmw.ac.uk
Background:
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.
Results:
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.
Conclusions:
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.