Effects of Aging and Nitrogen Deprivation on Nonfunctional rRNA Decay in Saccharomyces cerevisiae

Abstract

Nonfunctional Ribosomal RNA Decay (NRD) is a quality control pathway in Saccharomyces cerevisiae capable of degrading functionally defective mature rRNAs. Two types of NRD are known: 18S NRD which removes rRNAs with mutations in the small subunit decoding site and 25S NRD which removes rRNAs with mutations in the large subunit peptidyl transferase center. 18S NRD is translation dependent and occurs after ribosomal subunit joining on the mRNA. 25S NRD is mechanistically distinct; 25S rRNA degradation is translation independent and occurs prior to ribosomal subunit joining. We are interested in understanding this pathway because rRNAs are usually very abundant, generally comprising greater than 80% of the total cellular RNA, and very stable, with half‐lives on the order of several days. Therefore, natural NRD substrates in the form of damaged rRNAs may increase as cells age. Moreover, defective rRNAs may accumulate in NRD‐deficient cells. General ribosome turnover also increases under certain cellular stress conditions. For example, nitrogen deprivation results in degradation of both small and large ribosomal subunits by ribophagy. However, the effect of nitrogen starvation on NRD is unknown. Therefore, we are interested in analyzing the effects of both chronological aging and nitrogen deprivation on 18S and 25S NRD. To do this, we are measuring growth phenotypes and rRNA expression levels in yeast grown in normal or nutrient‐deprived media for various lengths of time. These experiments use either wild‐type or NRD‐deficient yeast strains transformed with rRNA expression plasmids that encode functional and/or nonfunctional versions of the 18S and 25S rRNAs. The plasmid‐derived rRNAs also contain short, unique sequence tags that allow for specific detection of these rRNAs in the presence of total cellular rRNA. Data collection and analysis are currently ongoing. We hope that these studies might provide insight into the accumulation of defective rRNAs over time in chronologically aged cells and the effects of nitrogen deprivation on this novel rRNA decay pathway.Support or Funding InformationThis work is supported by the Dr. G. Ashley Allen Student Research Grant at Washington and Lee University.