Department of Biological Chemistry, Weizmann Institute of Science, Rehovot
The synthesis of Inner Membrane Proteins (IMPs) requires co-translational insertion of hydrophobic domains into the membrane. During IMP translation the translating machinery contacts the membrane protein translocation channel. How is the IMP-translating ribosome nascent chain complex targeted to the membrane? The current model suggests that recognition and targeting of an IMP-translating complex to the membrane is mediated by the Signal Recognition Particle (SRP), which selects and interacts with the hydrophobic nascent chain. The SRP temporarily arrests translation and delivers the entire complex to the membrane, where co-translational insertion resumes through the protein translocation cannel. In contrast, in vivo studies have suggested a different order of events, during which IMP-encoding mRNAs are recognized and targeted to membrane-associated ribosomes. Our studies in E. coli identified a conserved RNA binding protein, which binds IMP-encoding mRNAs specifically and independently of translation.
