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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.

Describes the use of a novel genetic approach to elucidate the function of an essential signal recognition particle (SRP)-like particle in E. coli. Gene identification through genome-wide screen; Inhibition of the SRP pathway; Utilization of SRP-independent targeting pathway by E. coli preproteins and inner membrane proteins.