Abstract
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 language | English (US) |
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Article number | e04418 |
Journal | eLife |
Volume | 3 |
DOIs | |
State | Published - Oct 30 2014 |
Externally published | Yes |
Keywords
- 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