MPI Campus Seminar: Kinetics and Thermodynamics of –1 Ribosomal Frameshifting

MPI Campus Seminar

  • Datum: 29.01.2020
  • Uhrzeit: 12:00 - 13:00
  • Vortragende(r): Lars Bock
  • Department of Theoretical and Computational Biophysics
  • Ort: Max-Planck-Institut für biophysikalische Chemie (MPIBPC)
  • Raum: Large Seminar Room
  • Gastgeber: S. Glöggler, A. Godec, A. Faesen, J. Liepe, S. Meek, A. Stein, M. Wilczek, S. Karpitschka, D. Zwicker
  • Kontakt: stefan.gloeggler@mpibpc.mpg.de
MPI Campus Seminar: Kinetics and Thermodynamics of –1 Ribosomal Frameshifting
The ribosome synthesizes proteins according to mRNA blueprints by iteratively mapping three mRNA nucleotides to one amino acid with the help of tRNAs. Maintenance of this three-nucleotide reading frame is essential for the cell because errors can lead to the formation of non-functional proteins. Spontaneous reading frame changes are rare and occur with a frequency of < 10-5 per codon. However, specific mRNA sequences can guide the ribosome to shift the reading frame, thereby increasing the genomic information density. Programmed –1 ribosomal frameshifting, a shift by one nucleotide upstream, can occur while two tRNAs are bound to a slippery-sequence motif of the mRNA. Mutations of the slippery sequence have dramatic effects on the frameshift efficiency, but, up to now, a quantitative mechanical model was missing.
In our work, employing Bayesian statistics, we obtained free-energy differences of mRNA-tRNA base pairs in the 0, the original frame, and the –1 frame from the frameshift efficiencies of slippery-sequence variants of the dnaX gene. Our results show that frameshift efficiencies of other sequences can be predicted from the free-energy differences of the base pairs present in both frames. These free-energy differences determine the probability of ending up in either reading frame, because dnaX inhibits tRNA translocation to such a degree that the free-energy barrier hindering the reading-frame change is overcome during the translation pause. Furthermore, the obtained base-pair free energies allowed us to quantify the effect of ribosome environment on the strength of the base pairs. Finally, we confirmed the prediction of this model by showing that decreasing tRNA translocation rates result in higher frameshift efficiencies by measuring efficiencies in the presence of mutated elongation factor G. This quantitative model of frameshifting will enable the efficient identification of frameshift-prone sequences from genetic data.
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