Datensatz

Zusammenfassung

To survive under conditions of stress, such as nutrient deprivation, bacterial 70S ribosomes dimerize to form hibernating 100S particles(1). In gamma-proteobacteria, such as Escherichia coli, 100S formation requires the ribosome modulation factor (RMF) and the hibernation promoting factor (HPF)(2-4). Here we present single-particle cryo-electron microscopy structures of hibernating 70S and 100S particles isolated from stationary-phase E. coli cells at 3.0 angstrom and 7.9 angstrom resolution, respectively. The structures reveal the binding sites for HPF and RMF as well as the unexpected presence of deacylated E-site transfer RNA and ribosomal protein bS1. HPF interacts with the anticodon-stem-loop of the E-tRNA and occludes the binding site for the messenger RNA as well as A- and P-site tRNAs. RMF facilitates stabilization of a compact conformation of bS1, which together sequester the anti-Shine-Dalgarno sequence of the 16S ribosomal RNA (rRNA), thereby inhibiting translation initiation. At the dimerization interface, the C-terminus of uS2 probes the mRNA entrance channel of the symmetry-related particle, thus suggesting that dimerization inactivates ribosomes by blocking the binding of mRNA within the channel. The back-to-back E.coli 100S arrangement is distinct from 100S particles observed previously in Grampositive bacteria(5-8), and reveals a unique role for bS1 in translation regulation.