The native form of FtsA, a septal protein of Escherichia coli, is located in the cytoplasmic membrane.

Antisera able to recognize FtsA, one of the septal proteins of Escherichia coli, have been obtained and used to show that native FtsA, when expressed at levels ranging from physiological to induced from lambda pR, is located in the inner membrane. Experiments of trypsin accessibility to FtsA in membranes, spheroplasts, and vesicles indicated that FtsA is located such that it faces the cytoplasm. This location is consistent with current knowledge about the participation of FtsA in a molecular complex active in cell division called septator.