Identification of a second Mycobacterium tuberculosis gene cluster encoding proteins of an ABC phosphate transporter

Following the identification of a M. tuberculosis phosphate transporter belonging to the superfamily of ABC transporters, we report on the cloning and sequencing of two additional genes, called pstS-3 and pstC-2, encoding proteins homologous to PstS and PstC of Escherichia coli, respectively, Together with the previously isolated M. tuberculosis gene similar to the E. coli pstA, these are included in a cluster encoding a second putative phosphate transport system, We demonstrate that pstS-3 encodes the previously described Ag 88, a 40 kDa M, bovis BCG culture filtrate antigen (immunodominant in H-2(b) haplotype type mice), Finally, a signature motif identifying integral transmembrane proteins of prokaryotic phosphate binding-dependent permeases is proposed.