Distribution of the 12/40 polymorphism. (A). Schematic representation of PE_PGRS17 and PE_PGRS18 showing the distribution of the 12/40 polymorphism (red block) between paralogous and orthologous sequences. (B). Multiple sequence alignment of the 12/40 polymorphism region (highlighted with grey) in PE_PGRS17 and PE_PGRS18 of the three sequenced mycobacterial genomes of M. tuberculosis H37Rv (H37Rv), M. tuberculosis CDC1551 (CDC1551) and M. bovis AF2122/97 (M. bov AF2122/97). The corresponding sequences in M. tuberculosis strain H37Ra were determined by sequencing and proved to be identical to H37Rv. MAR: major alignable coding region.