Talk abstracts

Talk on Saturday 08:20-08:40am submitted by Shinichiro Shoji

Reverse translocation of tRNA in the ribosome

Shinichiro Shoji (Department of Microbiology, The Ohio State University), Sarah Walker (Department of Microbiology, The Ohio State University), Kurt Fredrick (Department of Microbiology, Ohio State Biochemistry Program, The Ohio State University)

Abstract:
A widely held view is that directional movement of tRNA in the ribosome is determined by an intrinsic mechanism and driven thermodynamically by transpeptidation. Here, we show that, in certain ribosomal complexes, the pretranslocation (PRE) state is favored over the posttranslocation (POST) state at equilibrium. Spontaneous and efficient conversion from the POST to PRE state is observed when EF-G is depleted from ribosomes in the POST state or when tRNA is added to the E site of ribosomes containing P-site tRNA. In the latter assay, the rate of tRNA movement is increased by streptomycin and neomycin, decreased by tetracycline, and not appreciable affected by the acylation state of the tRNA. In one case, we provide evidence that complex conversion occurs predominantly by reverse translocation (i.e., direct movement of the tRNAs from the E and P sites to the P and A sites, respectively). These findings have implications for the energetics of translocation.

Keywords: Ribosome, Translocation, Antibiotics