Figure 1.

Genomic organization of the PE and PPE genes associated with the Mycobacterium tuberculosis ESAT-6 (esx) gene clusters. Open reading frames are represented by blocked arrows indicating direction of transcription, with the different colors reflecting specific gene families and the length of the arrow reflecting the relative lengths of the genes. (A) Schematic representation of the PE and PPE genes situated within the ESAT-6 (esx) gene cluster regions. The vertical arrow indicates the direction of duplication of the ESAT-6 (esx) gene cluster regions, from region 4, 1, 3, 2 and lastly 5 in descending order. The positions of the PE (small arrow in light green) and PPE (larger arrow in yellow) genes are blocked, (B) Schematic representation of the PE and PPE genes duplicated from the ESAT-6 (esx) gene cluster regions, with the positions of the ESAT-6 and CFP-10 genes indicated, (C) Schematic representation of the PE and PPE genes associated with the ESAT-6 (esx) gene cluster regions (''associated with'' denotes genes which are hypothesized to have been duplicated from ESAT-6 (esx) gene cluster regions, as they are very homologous to their paralogues within the ESAT-6 (esx) gene clusters and have the same paired genomic orientation – see also Table 2).