Signal recognition particle mediated protein targeting in Escherichia coli

The signal recognition particle (SRP) is a conserved ribonucleoprotein comp lex that binds to targeting sequences in nascent secretory and membrane pro teins. The SRP guides these proteins to the cytoplasmic membrane in prokary otes and the endoplasmic reticulum membrane in eukaryotes via an interactio n with its cognate receptor. The E. coli SRP is relatively small and is cur rently used as a model for fundamental and applied studies on translation-l inked protein targeting. In this review recent advances in our understandin g of the structure and function of the E. coli SRP and its receptor are dis cussed. In particular, the interplay between the SRP pathway and other targ eting routes, the role of guanine nucleotides in cycling of the SRP and the substrate specificity of the SRP are highlighted.