Expression of Genes in Mycobacteria

Over the past 10 years, major advances have been made in the field of molecular mycobacterioiogy. These include the generation of shuttle vectors for use in both Escherichia coli and mycobacteria, electroporation protocols to introduce these plasmids into mycobacteria and promoter cassettes, which can be used to drive the expression of cloned genes in the mycobacterial host (1 –6 ). Similar procedures have been instrumental in the study of many aspects of prokaryotic biology but, in their absence, our understanding of basic processes within species of mycobacteria has been limited. Similarly, the ability to overexpress cloned genes in bacteria has been important in revealing the functions of a great diversity of heterologous proteins. Using Mycobacterium vaccae as the host, the available expression technology has allowed the overexpression, purification and crystallization of the Mycobacterium tuberculosis superoxide dismutase (5 ,7 ). The elucidation of the crystal structure of this important enzyme has yielded some very interesting information on protein structure and function in M . tuberculosis . Similarly, the glycosylation of mycobacterial proteins (which cannot be replicated in other bacterial hosts such as E. coli ) is being investigated using these expression systems (8 ,9 ). In order to benefit from the wealth of information being presented to the screntitic community in the what has been termed the “post-genomic era of microbiology,” the continued utilization and improvement of such methodology is of paramount importance,