Preferential interaction of Sec-G with Sec-E stabilizes an unstable Sec-E derivative in the Escherichia coli...

SecY, SecE and SecG form a membrane part of the protein translocation machinery. A SecG-overproducing plasmid was constructed by placing the secG gene under the control of the tac promoter. From the extent of SecG overproduction, the number of SecG molecules in one normal cell was estimated to be about 1,000, which is similar to those of SecY and SecE. Overproduction of SecG stabilized the overproduction of SecE-C, an unstable truncated derivative of SecE, as effectively as SecY does. SecG overproduction also stabilized the overproduction of SecY. However, the SecG-dependent stabilization of SecY was less potent than the SecE-dependent stabilization. These results indicate that SecG preferentially interacts with SecE, which associates with SecY, the SecG-SecE-SecY complex thus being formed in the cytoplasmic membrane.