SEPARABLE ATPASE AND MEMBRANE INSERTION DOMAINS OF THE SECA SUBUNIT OF PREPROTEIN

The SecA subunit of preprotein translocase drives ATP-dependent transl ocation of preproteins across the bacterial inner membrane concomitant with cycles of membrane insertion and de-insertion (Economou, A., and Wickner, W. (1994) Cell 78, 835-843). We have identified the membrane -inserting region of SecA as a 30-kDa domain in the C-terminal third o f the protein beginning at aminoacyl residue 610, Limited proteolysis in the absence of translocation ligands indicates that the SecA monome r is composed of two primary structural domains, the 30-kDa membrane-i nserting domain and an N-terminal 65-kDa ATPase domain This Limited pr otease treatment of SecA results in constitutive ATPase activity, indi cating that intramolecular constraints between the two domains mag pla y a role in the regulation of ATP hydrolysis by SecA.