An exported protein. Unlike its M.tuberculosis counterpart has poor pore forming ability in artificial liposomes, does not undergo conformational change at acidic pH (PubMed:23150662). Mutation of 2 residues to those found in M.tuberculosis (25-TA-26 to IH) alters the properties of this protein so that it inserts into liposomes at acidic pH, forming pores, like its M.tuberculosis counterpart (PubMed:26801203). Forms a tight 1:1 complex with EsxB (PubMed:19854905, PubMed:20085764, PubMed:23150662). An artificial EsxA-EsxB heterodimer interacts with EspA (PubMed:19854905). Probably secreted via the ESX-1 / type VII secretion system (T7SS). Accumulates in the cell and is secreted when grown in Saunton's medium, when grown in 7H9 medium protein only accumulates intracellularly (PubMed:15687187). No secretion of EsxB, very little EsxB protein accumulates intracellularly (PubMed:15687187). To improve over-expression in E.coli the proteins were cloned as a single protein in the (non-native) order esxA-esxB with a cleavable thrombin tag (PubMed:19854905). Belongs to the WXG100 family. ESAT-6 subfamily.