Figure 3. Schematic representation of the ESX-1 secretion system. (A) Schematic organization of the M. tuberculosis genomic region containing the RD1 genes. (B) Model. The abbreviation ecc stands for esx conserved component, whereas esp stands for ESX-1 secretion-associated proteins. The topology of the different proteins in the cytoplasmic membrane is shown and refers to the ESX-1 cluster based on predictions made using the MEMSAT3 algorithm. Note that the channel drawn in the outer membrane of this model refers to a hypothetical pore, whose existence has not been experimentally demonstrated. Reproduced from Bitter et al.¹⁷⁶