Title: Dynamics of Translation Elongation in an mRNA Context with a High Frameshifting Propensity
Description: Ribosomes are universally conserved macromolecular machines found within all living cells that catalyze protein synthesis, one of nature’s most fundamental processes. Ribosomes synthesize proteins, which are polymeric chains of amino acids, by incorporating the amino acids one at a time via aminoacylated-transfer RNAs (aa-tRNAs), based on translation of the sequence of triplet- nucleotide codons presented by the messenger RNA (mRNA) template that is a direct readout of genomic DNA. Recent biochemical, structural, dynamic, and computational studies have uncovered large-scale conformational changes of the ribosome, its tRNA substrates, and the additional protein translation factors that play important roles in regulating protein synthesis, especially during the elongation phase of translation when the bulk of each protein is synthesized. How the ribosome, its translation elongation factors, tRNAs, and mRNA physically coordinate and regulate the movements of the tRNAs carrying amino acids into, through, and out of the ribosome remains one of the more fundamental questions in the mechanistic studies of protein synthesis.

A complete understanding of the conformational dynamics of ribosomal complexes will improve our knowledge of how translation is regulated, including how ribosome-targeting antibiotics regulate translation elongation, and will provide crucial information for designing next-generation antibiotics. In this thesis I have investigated the conformational dynamics of the ribosome during the elongation phase of protein synthesis at the single-molecule level using single-molecule fluorescence resonance energy transfer (smFRET) microscopy experiments. Specifically, I have studied ribosomal dynamics during the elongation phase of translation in the presence of a tRNAPro in the context of an mRNA that has the propensity to shift out of the reading frame. My studies have revealed information about the mechanistic and regulatory functions of the posttranscriptional modifications of tRNAPro in a context in which the ribosomal complex has the propensity to undergo non-programmed +1-frameshifting, in which the tRNA-mRNA base pairing shifts one base toward the 3’ end of the mRNA, and if unchecked, leads to the synthesis of a polypeptide with a completely different sequence of amino acids.

My data suggests that in this context, the mechanism underlying non-programmed +1-frameshifting involves the tRNA shifting out of frame prior to the tRNA being accommodated in the P site, i.e. either while the tRNA is in the A site, or more likely, during translocation of the tRNA from the A site to the P site, and not while the tRNA is already occupying the P site, as previously proposed.