Characterization of mutant M. tuberculosis strains. A. PCR analysis showed Rv3763 to be absent from Δ19 and that this sequence had been successfully reintroduced into strains Δ19::19,, Δ19::19NA, and Δ19::19NOG. B. Western Blotting of cellular pellet indicating that the 19 kDa is not produced in Δ19 (lane 2). Expression of native protein of the same MW is restored close to normal levels by reintroduction of the 19 kDa gene in strain Δ19::19. C. Analysis of pellet and culture supernatant of complemented mutant strains. 19 kDa protein was only detected in the supernatant of cultures of the non-acylated (NA) and non-O- glycosylated complemented strains and was of slightly lower MW than the native 19 kDa.