Controlling gene expression in mycobacteria.

The genus mycobacterium contains some of the most important human pathogens, including Mycobacterium tuberculosis, which causes tuberculosis in approximately 8 million people annually; Mycobacterium leprae, the etiologic agent of leprosy, which affects millions of people in Asia, Africa and Latin America; and Mycobacterium bovis, which causes tuberculosis in animals and people. Genetic tools for mycobacteria have been developed during the last 15 years and have helped to improve our understanding of the biology and pathogenesis of mycobacteria. However, genetic switches have only recently been developed that allow control of mycobacterial gene expression. Such systems have been used to facilitate protein overexpression in mycobacteria and to analyze gene function, in particular functions of essential genes. Some of the recently developed systems will allow controlling gene expression during animal infections and may therefore become invaluable tools for drug target validation. This article will review the features of available mycobacterial genetic switches and discuss their applications.