Required for secretion of EsxA (ESAT-6) and EsxB (CFP-10) and for virulence. Involved in translocation of bacteria from the host (human) phagolysosome to the host cytoplasm (PubMed:17604718). Homodimer; disulfide-linked (PubMed:20585630). An artificial EsxB-EsxA heterodimer interacts with EspA (PubMed:19854905). Secreted via the ESX-1 / type VII secretion system (T7SS) (PubMed:16030141). Secretion of EspA, EsxA and EsxB is mutually dependent (PubMed:16030141). Transcriptionally activated by EspR (PubMed:18685700, PubMed:22389481, PubMed:25536998). Repressed by the MprB/MprA two-component system, by direct regulation and via EspR (PubMed:23104803, PubMed:25536998). Up-regulated by the PhoP/PhoR two-component system, via EspR (PubMed:16573683, PubMed:25536998). Deletion mutants fail to secrete EsxA and EsxB, and are as attenuated as ESX-1 mutants in virulence assays (PubMed:16030141). Bacteria no longer translocate from the phagolysosome to the cytosol of host (human) cells; bacteria replicate in phagolysosome (PubMed:17604718). Host (human) cells no longer produce cytokine IP-10 (CXCL10) upon infection, but continue to produce IL-1 beta (IL1B) (PubMed:26048138). Maintenance of wild-type levels of EspA requires both EspC and EspD. Has been postulated to mediate virulence through maintenance of mycobacterial cell surface integrity (PubMed:20585630), but studies of detergent sensitivity of various strains and mutants indicate that EspACD and ESX-1 deficiency does not impact the cell surface integrity (PubMed:24078612).