Expression of Mycobacterium leprae genes from a Streptococcus mutans promoter in Escherichia coli K-12

Genomic libraries of Mycobacterium leprae DNA partially digested with Pst I were constructed in the expression vector pYA626, which contains the promoter region from the Streptococcus mutans gene encoding aspartate beta-semialdehyde dehydrogenase, which is very efficiently expressed in Escherichia coli. We have detected several clones that complement a mutation in the citrate synthase gene of E. coli. Southern blot analysis demonstrated that the complementing DNA was M. leprae DNA. Sodium dodecyl sulfate/polyacrylamide gel analysis of polypeptides produced by minicells containing the citrate synthase-complementing recombinant molecules demonstrated the production of a 46-kDa polypeptide. When the citrate synthase-complementing fragment was cloned in pYA626 in the reverse orientation, the recombinant molecule was no longer able to complement the mutation in the citrate synthase gene and no longer produced the 46-kDa polypeptide. When the DNA fragment was cloned in the Pst I site of pHC79, so as to allow expression from the beta-lactamase promoter, the resulting recombinant failed to complement the mutation in the E. coli citrate synthase gene yet still produced the 46-kDa polypeptide, but in one-fourth the amount than when expressed from the S. mutans asd promoters. This demonstrates that M. leprae translational sequences can be recognized by E. coli translational machinery. Promoter expression vectors can be used to obtain expression of protein antigens to be used for early diagnosis of leprosy or components of a vaccine and proteins that are targets of potential antileprosy drugs.