Isolation, characterization, and molecular cloning of a specific Mycobacterium tuberculosis antigen gene: identification of a species-specific sequence.

A rabbit polyclonal antiserum exhibiting a specific recognition pattern for Mycobacterium tuberculosis proteins was used to screen an M. tuberculosis genomic library constructed in the expression vector lambda gt11. One clone, denominated C1:10, expressed M. tuberculosis-specific determinants as part of a large fusion protein with beta-galactosidase. The gene for this protein has been sequenced, and it encodes a protein of 134 amino acids (13.8 kDa) which did not display significant homology with any of the previously reported proteins in the data bases. Hybridization studies with restriction fragments of the cloned sequence revealed that it was not present in the genomes of related mycobacteria, namely, M. bovis, M. bovis BCG, M. flavescens, M. fortuitum, M. phlei, and M. vaccae. These findings suggest that we have detected a gene, or a fragment therefrom, unique for M. tuberculosis whose nucleotide and amino acid sequences could be useful tools in the design of an improved vaccine or a diagnostic method of greater accuracy for tuberculosis.