Escherichia coli SecY and SecE proteins appear insufficient to constitute the SecA receptor

In order to test whether SecY and SecE proteins constitute the SecA receptor inside out membrane vesicles where prepared from strains producing greatly different levels of these two proteins, and their SecA binding activity was quantitated. Substantial overproduction of SecE or SecY and SecE proteins resulted in no increase or only 50% increase, respectively, in the number of high affinity SecA binding sites. These results suggest that SecY and SecE proteins appear insufficient to constitute the primary SecA receptor. The existence of a cycle of SecA association with the inner membrane and its modulation by particular integral membrane proteins is discussed.