Project description:Ribosome profiling study of dom34 and hbs1 knockout strains using short (16-nt) and long (28-nt) monosome-protected footprints and disome-protected footprints
Project description:During translation elongation, the ribosome ratchets along its mRNA template, incorporating each new amino acid and translocating from one codon to the next. The elongation cycle requires dramatic structural rearrangements of the ribosome. We show here that deep sequencing of ribosome-protected mRNA fragments reveals not only the position of each ribosome but also, unexpectedly, its particular stage of the elongation cycle. Sequencing reveals two distinct populations of ribosome footprints, 28-30 nucleotides and 20-22 nucleotides long, representing translating ribosomes in distinct states, differentially stabilized by specific elongation inhibitors. We find that the balance of small and large footprints varies by codon and is correlated with translation speed. The ability to visualize conformational changes in the ribosome during elongation, at single-codon resolution, provides a new way to study the detailed kinetics of translation and a new probe with which to identify the factors that affect each step in the elongation cycle. Ribosome profiling, or sequencing of ribosome-protected mRNA fragments, in yeast. We assay ribosome footprint sizes and positions in three conditions: untreated yeast (3 replicates) and yeast treated with translation inhibitors cycloheximide (2 replicates) and anisomycin (2 biological replicates, one technical replicate). We also treat yeast with 3-aminotriazole to measure the effect of limited histidine tRNAs on ribosome footprint size and distribution (two treatment durations).
Project description:Ribosomes that stall before completing peptide synthesis must be recycled and returned to the cytoplasmic pool. The protein Dom34 and cofactors Hbs1 and Rli1 can dissociate stalled ribosomes in vitro, but the identity of targets in the cell is unknown. Here we use ribosome profiling methodology to reveal a high- resolution molecular characterization of Dom34 function in vivo. We show that Dom34 removes stalled ribosomes from mRNAs that are truncated but, in contrast, does not generally dissociate ribosomes on coding sequences known to trigger stalling, such as polyproline. We also show that Dom34 targets arrested ribosomes near the ends of 3 ? UTRs. These ribosomes appear to gain access to the 3 ? UTR via a mechanism that does not require decoding of the mRNA. These results suggest that Dom34 carries out the important task of rescuing ribosomes found in noncoding regions. 25 samples are included in the study (2 mRNA-Seq samples and 23 ribosome footprint profiling samples). These include wild-type and dom34 or hbs1 knockout strains that were created in a variety of genetic backgrounds, treated with various agents in cell culture (e.g. diamide, 3-AT, or glucose starvation), treated differently during cell lysis (use of cycloheximide vs. other ribosome-stabilizing agents), or prepared in different ways after cell lysis (e.g. retention of short vs. long monosome-protected footprints or disome footprints).
