Cell Biology

Separating the Haves from the Have-Nots

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Science  21 Nov 2003:
Vol. 302, Issue 5649, pp. 1297
DOI: 10.1126/science.302.5649.1297c

Proteins destined for insertion into or across a membrane carry a sequence, usually at the N terminus, that distinguishes them from soluble cytosolic proteins. The signal sequence interacts with the targeting machinery and the protein translocation apparatus, called the translocon, which actively transports the polypeptide chain across the membrane. In Escherichia coli, the SecA protein binds to the signal sequence on nascent secretory proteins, maintains them in an unfolded and translocation-competent state, and carries them to the translocon for export. Eser and Ehrmann describe how SecA plays an additional chaperone-like function by acting as a quality-control sensor: SecA binds to proteins that lack signal sequences and promotes their folding, thus helping to divert them away from the translocon. — SMH

Proc. Natl. Acad. Sci. U.S.A. 100, 13231 (2003).

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