Elongation arrest is a physiologically important function of signal recognition particle

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Abstract
Signal recognition particle (SRP) targets proteins for co‐translational insertion through or into the endoplasmic reticulum membrane. Mammalian SRP slows nascent chain elongation by the ribosome during targeting in vitro . This ‘elongation arrest’ activity requires the SRP9/14 subunit of the particle and interactions of the C‐terminus of SRP14. We have purified SRP from Saccharomyces cerevisiae and demonstrated that it too has elongation arrest activity. A yeast SRP containing Srp14p truncated at its C‐terminus (ΔC29) did not maintain elongation arrest, was substantially deficient in promoting translocation and interfered with targeting by wild‐type SRP. In vivo , this mutation conferred a constitutive defect in the coupling of protein translation and translocation and temperature‐sensitive growth, but only a slight defect in protein translocation. In combination, these data indicate that the primary defect in SRP ΔC29 is in elongation arrest, and that this is a physiologically important and conserved function of eukaryotic SRP.