Rapid binding and release of Hfq from ternary complexes during RNA annealing

Julia F. Hopkins, Subrata Panja, Sarah A. Woodson

Research output: Contribution to journalArticlepeer-review

52 Scopus citations


The Sm protein Hfq binds small non-coding RNA (sRNAs) in bacteria and facilitates their base pairing with mRNA targets. Molecular beacons and a 16nt RNA derived from the Hfq binding site in DsrA sRNA were used to investigate how Hfq accelerates base pairing between complementary strands of RNA. Stopped-flow fluorescence experiments showed that annealing became faster with Hfq concentration but was impaired by mutations in RNA binding sites on either face of the Hfq ring or by competition with excess RNA substrate. A fast bimolecular Hfq binding step (∼10 8M -1s -1) observed with Cy3-Hfq was followed by a slow transition (0.5s -1) to a stable Hfq-RNA complex that exchanges RNA ligands more slowly. Release of Hfq upon addition of complementary RNA was faster than duplex formation, suggesting that the nucleic acid strands dissociate from Hfq before base pairing is complete. A working model is presented in which rapid co-binding and release of two RNA strands from the Hfq ternary complex accelerates helix initiation 10000 times above the Hfq-independent rate. Thus, Hfq acts to overcome barriers to helix initiation, but the net reaction flux depends on how tightly Hfq binds the reactants and products and the potential for unproductive binding interactions.

Original languageEnglish (US)
Pages (from-to)5193-5202
Number of pages10
JournalNucleic acids research
Issue number12
StatePublished - Jul 2011
Externally publishedYes

ASJC Scopus subject areas

  • Genetics


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