Part of the ESX-1 / type VII specialized secretion system (T7SS), which exports several proteins including EsxA and EsxB (PubMed:15687187). Specific chaperone for cognate PE/PPE proteins, plays an important role in preventing aggregation of PE/PPE dimers (By similarity). Also plays a role in DNA conjugation, in at least recipient strain (By similarity). Interacts specifically with ESX-1-dependent PE/PPE proteins (By similarity). EsxA and EsxB secretion severely reduced, but not their expression (PubMed:15687187). Belongs to the EspG family. Truncated N-terminus.