The E. coli signal recognition particle is required for the insertion of a subset of inner membrane proteins

A genome-wide screen was designed to determine the genes that encode signal recognition particle (SRP) substrates in Escherichia coli. Inhibition of the SRP pathway strongly blocked the membrane insertion of several polytopic inner membrane proteins (IMPs) that were expected to be SRP substrates, but had a smaller impact on the insertion of other IMPs and no discernible effect on preprotein translocation. Findings indicated that although most E. coli preproteins and some IMPs can use SRP-independent targeting pathways effectively, the structural features of a subset of IMPs need the conservation of an SRP-based targeting mechanism.