Members of the evolutionary conserved Oxa1/Alb3/YidC family have been shown to play an important role in membrane protein insertion, folding and/or assembly. Bacillus subtilis contains two YidC-like proteins, denoted as SpoIIIJ and YqjG. SpoIIIJ and YqjG are largely exchangeable, but SpoIIIJ is essential for spore formation and YqjG cannot complement this activity. To elucidate the role of YqjG, we determined the membrane proteome and functional aspects of B. subtilis cells devoid of SpoIIIJ, YqjG or both. The data show that SpoIIIJ and YqjG have complementary functions in membrane protein insertion and assembly. The reduced levels of F(1)F(O) ATP synthase in cells devoid of both SpoIIIJ and YqjG are due to a defective assembly of the F(1)-domain onto the F(0)-domain. Importantly, for the first time, a specific function is demonstrated for YqjG in genetic competence development.

The YidC/OxaI/Alb3 family of membrane proteins is involved in the biogenesis of integral membrane proteins in bacteria, mitochondria, and chloroplasts. Gram-positive bacteria often contain multiple YidC paralogs that can be subdivided into two major classes, namely, YidC1 and YidC2. The Streptococcus mutans YidC1 and YidC2 proteins possess C-terminal tails that differ in charges (؉9 and ؉ 14) and lengths (33 and 61 amino acids). The longer YidC2 C terminus bears a resemblance to the C-terminal ribosome-binding domain of the mitochondrial OxaI protein and, in contrast to the shorter YidC1 C terminus, can mediate the interaction with mitochondrial ribosomes. These observations have led to the suggestion that YidC1 and YidC2 differ in their abilities to interact with ribosomes. However, the interaction with bacterial translating ribosomes has never been addressed. Here we demonstrate that Escherichia coli ribosomes are able to interact with both YidC1 and YidC2. The interaction is stimulated by the presence of a nascent membrane protein substrate and abolished upon deletion of the C-terminal tail, which also abrogates the YidC-dependent membrane insertion of subunit c of the F 1 F 0 -ATPase into the membrane. It is concluded that both YidC1 and YidC2 interact with ribosomes, suggesting that the modes of membrane insertion by these membrane insertases are similar.