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Ribosome profiling and RNA-seq of an acute glucose starvation timecourse and 5 day growth course in S. cerevisiae

ABSTRACT: Ribosome profiling provides an opportunity to not only assess how the relative abundance of ribosome association with mRNAs changes in different conditions, but to look more closely at where along mRNAs those ribosomes bind. Here, we used ribosome profiling to calculate the ribosome polarity scores and changes in ribosome footprint read density in both aggregate and gene-specific ways. We profiled a time course of acute glucose starvation followed by glucose readdition and a multi-day growth course through the diauxic shift into stationary phase. We found that ribosome polarity became positive in postdiauxic shift conditions relative to log phase. In acute starvation, polarity shifted positive at our earliest time points but did not continue to do so at later time points. This is consistent with a read density analysis which demonstrated increased density on the 3’ half of genes after glucose starvation. Additionally, we performed ribosome profiling in samples that had glucose added back following acute starvation and observed a wave of new ribosome movement near the start codon and approximately 2,000 nucleotides downstream on open reading frames after one and five minutes of readdition, respectively. Our ribosome profiling analysis suggested that elongation slows during starvation which leads to a buildup of ribosomes on the 3’ halves of mRNAs. Further, it also indicated ribosomes previously built up can resume translation upon glucose readdition. We used reporter assays to corroborate these findings in vivo. Together, these results demonstrate how yeast regulate translation in response to glucose starvation.

ORGANISM(S): Saccharomyces cerevisiae

PROVIDER: GSE200491 | GEO | 2022/04/11

REPOSITORIES: GEO

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Project description:We use mRNA-seq in combination with polysome profiling to determine translational status for all mRNAs in Drosophila mature oocytes and activated eggs. Puromycin-treated lysates are used as a negative control in polysome profiling experiments. Additionally, we use ribosome footprinting to globally measure translational efficiency of mRNAs in wild type mature oocytes as well as wild type and png mutant activated eggs. Lysates of hand-dissected Drosophila mature oocytes (containing ~540 M-NM-<g of total RNA) were subjected to separation by velocity sedimentation through sucrose gradients. In this way, free mRNAs (present in RNPs fraction) or those comigrating with ribosomal subunits (40S or 60S+80S fractions) or with varying numbers of bound ribosomes (low polysomes (2-4 ribosomes), medium polysomes (5-9 ribosomes), and heavy polysomes (more than 10 ribosomes) can be separated based on their size and collected as sucrose gradient fractions. To compare quantitatively the levels of every mRNA across the polysome gradient fractions, we added 5ng of S. cerevisiae mRNA as an exogenous spike-in to each of the six fractions of interest: RNPs, 40S, 60S+80S, low polysomes, medium polysomes and heavy polysomes. RNA was extraced from these fractions, follwing proteinase K treatment, by hot acid phenol method. In case of unfractionated lysates, RNA was extracted using TRIzol (Invitrogen) according to manufacturerM-bM-^@M-^Ys instructions. mRNA-seq samples were prepared from 1 M-NM-<g of total RNA (in case of sucrose gradient fractions and unfractionated lysates) and subject to Illumina based sequencing. Puromycin-treated lysates of mature oocytes or 0-2h Drosophila activated eggs (containing ~540 M-NM-<g of total RNA) were also subjected to separation by velocity sedimentation through sucrose gradients. Puromycin causes premature termination of elongating ribosomes and thus it can be used to determine whether the mRNAs co-sedimenting with the polysomal peaks (defined here as M-bM-^IM-%5 ribosomes) were actively engaged in translation. As an independent approach to assess translation and obtain information on the position of ribosomes on mRNAs, we employed ribosome footprinting. In addition to analyzing the same samples, as by polysome profiling, we also analyzed png mutant activated eggs by ribosome footprinting. Ribosome footprint profiling measures the number of ribosome-protected fragments (RPFs) derived from the mRNAs of each gene, resulting in a singular value of translational efficiency (TE) for each gene (TE=RPF/RNA).

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Ribosome profiling and RNA-seq of an acute glucose starvation timecourse and 5 day growth course in S. cerevisiae

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