Expression of Mycobacterium tuberculosis genes in Escherichia coli

Two Escherichia coli clones expressing Mycobacterium tuberculosis antigens were isolated from a gene-bank in the plasmid vector pBR 325. ‘Western blot’ analysis revealed the presence of a unique protein band of molecular weight 68,000 and 38,000, respectively in cell extracts from each clone. The 68,000 dalton antigen was found to be expressed on Escherichia coli outer surface. Plasmid DNA from a third clone could confer leucine independence on two different leu B mutants of Escherichia coli but not on mutants in other leu genes, pointing to the possibility of genetic complementation. Thus, Mycobacterium tuberculosis DNA is capable of expression in Escherichia coli