Component of the type VII secretion system (Ess). Required for the secretion of substrates including EsxA and EsxB. However, unable to support secretion of the substrate protein EsxC. Homooligomer. Interacts with EsaE. The N-terminal region is composed of two iterations of forkhead-associated (FHA) domain-like structures, which could interact with other proteins in the Esx secretion system. Belongs to the EssC family.