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 re ceptor inside out membrane vesicles where prepared from strains produc ing greatly different levels of these two proteins, and their SecA bin ding activity was quantitated. Substantial overproduction of SecE or S ecY and SecE proteins resulted in no increase or only 50% increase, re spectively, in the number of high affinity SecA binding sites. These r esults suggest that SecY and SecE proteins appear insufficient to cons titute the primary SecA receptor. The existence of a cycle of SecA ass ociation with the inner membrane and its modulation by particular inte gral membrane proteins is discussed.