Polysome-associated mRNA levels upon glucose repletion

Cell survival in changing environments requires appropriate regulation of gene expression, including post-transcriptional gene regulatory mechanisms. Based on reporter gene studies in glucose-starved yeast, it was proposed that translationally silenced eukaryotic mRNAs accumulate in P-bodies and can return to active translation. We present evidence contradicting the notion that this model is a widespread and general phenomenon. First, genome-wide measurements of mRNA abundance, translation, and ribosome occupancy following glucose withdrawal show that most mRNAs are lost from the cell coincident with their loss from polysomes. Second, only a very limited sub-population of translationally repressed transcripts, comprising fewer than 400 genes, can be reactivated for translation upon glucose re-addition in the absence of new transcription. This highly selective post-transcriptional regulation could be a mechanism for cells to minimize the energetic costs of reversing gene-regulatory decisions in rapidly changing environments by transiently preserving a pool of transcripts whose translation is rate-limiting for growth. Sigma 1278b yeast were grown to OD600=1.0-1.1 in YPD in baffled flasks at 30C with vigorous shaking. Cells were treated with thiolutin to a final concentration of 3ug/mL, harvested by centrifugation, and resuspended in pre-warmed YPA medium lacking glucose. Cells were returned to 30C for shaking for 10 minutes. For the refed samples, glucose was added to a final concentration of 2% and samples were taken after 5 minutes. Polysome preparation and RNA isolation were as described in Experimental Procedues. A common RNA sample, polysomal RNA from cells grown in YPD, was used for one channel of each array.