SecA is an intrinsic subunit of the Escherichia coli preprotein translocase and exposes its carboxyl terminus to the periplasm

Abstract

Summary SecA is the dissociable ATPase subunit of the Escheri- chia coli preprotein translocase, and cycles in a nucleo- tide-modulated manner between the cytosol and the membrane. Overproduction of the integral subunits of the translocase, the SecY, SecE and SecG polypep- tides, results in an increased level of membrane- bound SecA. This fraction of Sec A is firmly associated with the membrane as it is resistant to extraction with the chaotropic agent urea, and appears to be anchored by SecYEG rather than by lipids. Topology analysis of this membrane-associated form of Sec A indicates that it exposes a carboxy-terminal domain to the periplas- mic face of the membrane.