A variable number of tandem repeats result in polymorphic alpha -isopropylmalate synthase in Mycobacterium tuberculosis.

A locus of variable number of the tandem repeat, VNTR4155, resides in the putative leuA gene, encoding for alpha -isopropylmalate synthase (alpha -IPMS) of Mycobacterium tuberculosis, a repeat that is unique to the bacterium. The objective was to determine whether the polymorphic VNTR4155 was translated and resulted in a polymorphic protein. The putative leuA gene of the M. tuberculosis H37Rv strain was cloned by PCR and expressed in a His-tagged form in Escherichia coli. The enzymatic properties of the purified protein were studied. The protein was used as an antigen to immunize rabbits. Soluble proteins of several strains of M. tuberculosis were examined by Western blot analysis. The polymorphism of VNTR4155 was due to the presence of different copy number of the 57-bp tandem repeat. The putative alpha -IPMS of various strains of M. tuberculosis had different sizes, varying directly with the length of their VNTR4155. Copyright 2002 Elsevier Science Ltd. All rights reserved.