A SPECIES-SPECIFIC NUCLEOTIDE-SEQUENCE OF MYCOBACTERIUM-TUBERCULOSIS ENCODES A PROTEIN THAT EXHIBITS HEMOLYTIC-ACTIVITY WHEN EXPRESSED IN ESCHERICHIA-COLI

Species-specific proteins may be implicated in the unique pathogenic m echanisms characteristic of Mycobacterium tuberculosis. In previous st udies, a 3.0-kb species-specific DNA fragment of M. tuberculosis was i dentified (C. A. Parra, L. P. Londono, P. del Portillo, and M. E. Pata rroyo, Infect. Immun. 59:3411-3417, 1991). The nucleotide sequence of this 3.0-kb fragment has been obtained. This sequence was shown to con tain two open reading frames (ORFs) whose putative gene products share 68.9% identity between each other. The major ORF shows 57.8% similari ty,vith PLC-N and 53.2% similarity with PLC-B, two phospholipase C enz ymes from Pseudomonas aeruginosa. The major ORF was amplified by PCR a nd cloned into the pGEX-5T expression vector. Cell extracts of Escheri chia coli overexpressing this glutathione S-transferase fusion protein were shown to produce beta-hemolysis suggestive of phospholipase acti vity. Since phospholipase C enzymes have been reported as virulence fa ctors of P. aeruginosa and also of the intracellular pathogen Listeria monocytogenes, it is possible that the proteins identified in this st udy could also play a role in sustaining tuberculosis infection in hum ans.