Real-time observation of signal recognition particle binding to actively translating ribosomes

Thomas R. Noriega, Jin Chen, Peter Walter, Joseph D. Puglisi

Research output: Contribution to journalArticlepeer-review

34 Scopus citations


The signal recognition particle (SRP) directs translating ribosome-nascent chain complexes (RNCs) that display a signal sequence to protein translocation channels in target membranes. All previous work on the initial step of the targeting reaction, when SRP binds to RNCs, used stalled and non-translating RNCs. This meant that an important dimension of the co-translational process remained unstudied. We apply single-molecule fluorescence measurements to observe directly and in real-time E. coli SRP binding to actively translating RNCs. We show at physiologically relevant SRP concentrations that SRP-RNC association and dissociation rates depend on nascent chain length and the exposure of a functional signal sequence outside the ribosome. Our results resolve a long-standing question: how can a limited, sub-stoichiometric pool of cellular SRP effectively distinguish RNCs displaying a signal sequence from those that are not? The answer is strikingly simple: as originally proposed, SRP only stably engages translating RNCs exposing a functional signal sequence.

Original languageEnglish (US)
Article numbere04418
StatePublished - Oct 30 2014
Externally publishedYes


  • E. coli
  • biophysics
  • cell biology
  • protein targeting
  • ribosome translation
  • signal recognition particle
  • single molecule fluorescence
  • structural biology

ASJC Scopus subject areas

  • General Neuroscience
  • General Immunology and Microbiology
  • General Biochemistry, Genetics and Molecular Biology


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