type IV secretion system https://en.wikipedia.org/wiki/Secretion http://db-mml.sjtu.edu.cn/SecReT4/ Meng LIU (Mia), Oliver He T4SS are cell envelope-spanning complexes that form a channel through which DNA and proteins can travel from the cytoplasm of the donor cell to the cytoplasm of the recipient cell. T4SS is one of important secretion systems and usually consists of several components: mating-pair formation proteins (MPFs), which serve to establish physical contacts with a recipient bacterium; and, finally, a coupling protein (T4cp), which binds MOB and ssDNA to MPF . system