Part of the Sec protein translocase complex. Interacts with the SecYEG preprotein conducting channel. Has a central role in coupling the hydrolysis of ATP to the transfer of proteins into and across the cell membrane, serving as an ATP-driven molecular motor driving the stepwise translocation of polypeptide chains across the membrane. ATP + H2O + cellular proteinSide 1 = ADP + phosphate + cellular proteinSide 2. May bind 1 zinc ion per subunit. Monomer and homodimer. Part of the essential Sec protein translocation apparatus which comprises SecA, SecYEG and auxiliary proteins SecDF-YajC and YidC. Distribution is 50-50. Belongs to the SecA family. Truncated N-terminus.