Regulated Expression Systems for Mycobacteria and Their Applications

For bacterial model organisms like Escherichia coli and Bacillus subtilis, genetic tools to experimentally manipulate the activity of individual genes have existed for decades. But for genetically less tractable yet medically important bacteria such as Mycobacterium tuberculosis, such tools have rarely been available. More recently, several groups developed genetic switches that function efficiently in M. tuberculosis and other mycobacteria. Together these systems utilize six transcription factors, eight regulated promoters, and three regulatory principles. In this chapter we describe their design features, review their main applications, and discuss the advantages and disadvantages of regulating transcription, translation, or protein stability for controlling gene activities in bacteria. Genetic elements that enable specific and quantitative control over the activity of individual genes are irreplaceable components of the modern genetic toolbox. They facilitate not only the purification of proteins for biochemical, structural, or immunological studies but can also be applied to improve our understanding of in vivo gene functions. Until recently, only one such tool was available for use in mycobacteria, and its applicability in slowly growing mycobacteria was limited. But during the last decade at least a dozen new systems have been developed. In this chapter we review the design, components, and regulatory mechanisms of the different systems and discuss their main applications.