Many studies have established the mechanism of translocation of presecretory proteins across the cytoplasmic membrane of Escherichia coli. Translocation requires two kinds of proteins, soluble chaperone and membrane bound translocase. Sec B. the major chaperone, forms a complex with preproteins. Translocase consists of several peripheral and integral membrane proteins-Sec A, Sec E, Sec Y, Sec D and Sec F. Translocation also needs two kinds of energies, ATP and proton motive force (△μH^{+}).