A conserved function of YidC in the biogenesis of respiratory chain complexes.

The Escherichia coli inner membrane protein (IMP) YidC is involved in the membrane integration of IMPs both in concert with and independently from the Sec translocase. YidC seems to be dispensable for the assembly of Sec-dependent IMPs, and so far it has been shown to be essential only for the proper Sec-independent integration of some phage coat proteins. Here, we studied the physiological consequences of YidC depletion in an effort to understand the essential function of YidC. The loss of YidC rapidly and specifically induced the Psp stress response, which is accompanied by a reduction of the proton-motive force. This reduction is due to defects in the functional assembly of cytochrome o oxidase and the F(1)F(o) ATPase complex, which is reminiscent of the effects of mutations in the yidC homologue OXA1 in the yeast mitochondrial inner membrane. The integration of CyoA (subunit II of the cytochrome o oxidase) and F(o)c (membrane subunit of the F(1)F(o) ATPase) appeared exceptionally sensitive to depletion of YidC, suggesting that these IMPs are natural substrates of a membrane integration and assembly pathway in which YidC plays an exclusive or at least a pivotal role.