FIGURE 2.

Inhibition of the folding of synthesized Sec substrate proteins by molecular chaperones and posttranslational modifications. Fully synthesized Sec substrate proteins (or domains of Sec substrate proteins) are prevented from folding stably in the cytoplasm by molecular chaperones, such as (A) SecB, (B) DnaK or DnaJ, and (C) GroELS. Alternatively, many Sec substrate proteins require posttranslational modification that can only be made in the periplasm to fold stably, such as (D) disulfide bonds and (E) proteolytic removal of the N-terminal signal sequence.