Anionic Phospholipids Stabilize RecA Filament Bundles in Escherichia coli

We characterize the interaction of RecA with membranes in vivo and in vitro and demonstrate that RecA binds tightly to the anionic phospholipids cardiolipin (CL) and phosphatidylglycerol (PG). Using computational models, we identify two regions of RecA that interact with PG and CL: (1) the N-terminal helix and (2) loop L2. Mutating these regions decreased the affinity of RecA to PG and CL in vitro. Using 3D super-resolution microscopy, we demonstrate that depleting Escherichia coli PG and CL altered the localization of RecA foci and hindered the formation of RecA filament bundles. Consequently, E. coli cells lacking aPLs fail to initiate a robust SOS response after DNA damage, indicating that the membrane acts as a scaffold for nucleating the formation of RecA filament bundles and plays an important role in the SOS response.