Abstract: A process for replacing a nucleotide sequence in the genome of a mycobacterium strain comprises the steps of:a) providing a vector containing SacB gene coding for levane saccharase enzyme and a nucleotide sequence of interest;b) transfecting the mycobacterium strain with the vector;c) selecting clones of the resulting transfected mycobacteria for replacement of the nucleotide sequence of interest by propagating the transfected clones in a culture medium supplemented with sucrose; andd) isolating the recombinant strain.The process is useful for positive selection of allelic exchange mutants, such as in Mycobacterium tuberculosis complex.

Abstract: The present invention relates to the isolation of a new gene, des, which encodes a M. tuberculosis protein named DES. The des gene appears to be conserved among different Mycobacteria species. The amino acid sequence of the DES protein contains two sets of motifs that are characteristic of the active sites of enzymes from the class II diiron-oxo protein family. Among this family of proteins, DES shares significant homology with soluble stearoyl-ACP desaturases. DES is a highly antigenic protein, which is recognized by human sera from patients infected with M. tuberculosis and M. leprae but not by sera from tuberculous cattle. Thus, the DES protein provides a useful tool for the serodiagnostic analysis of tuberculosis.