CHARACTERIZATION OF THE MYCOBACTERIUM-TUBERCULOSIS ERP GENE ENCODING A POTENTIAL CELL-SURFACE PROTEIN WITH REPETITIVE STRUCTURES

Using the phoA gene fusion methodology adapted to mycobacteria, severa l Mycobacterium tuberculosis DNA fragments encoding exported proteins were recently identified. In this paper, the molecular cloning, genomi c positioning, nucleotide sequence determination and transcriptional s tart site mapping of a new M. tuberculosis gene, identified by this me thodology, are reported. This gene was called erp (for exported repeti tive protein) and has a sequence similar to that of the Mycobacterium leprae 28 kDa antigen irg gene M. tuberculosis erp gene contains a put ative iron box close to the mapped transcriptional start site. The pre dicted Erp protein displays a typical N-terminal signal sequence, a hy drophobic domain at the C-terminus and harbours repeated amino acid mo tifs. These structural features are reminiscent of cell-wall-associate d surface proteins from Gram-positive bacteria. We found that these re peats are conserved among M. tuberculosis isolates, and are absent fro m the published M. leprae irg gene sequence. In addition to being pres ent in M. leprae, erp sequences were found in other members of the M. tuberculosis complex, but not in other mycobacteria tested. These resu lts suggest that erp might encode a cell surface component shared by m ajor pathogenic mycobacteria.