The Effect of Ultraviolet Stress on Nonfunctional rRNA Decay

Abstract

Nonfunctional Ribosomal RNA Decay (NRD) is a quality control pathway that degrades structurally intact but functionally defective rRNAs. To date, there are two recognized NRD pathways in S. cerevisiae: 18S NRD and 25S NRD. These pathways are responsible for degrading nonfunctional 18S rRNAs and the 25S rRNAs respectively. 18S NRD is translation dependent and involves the translation factor‐like protein Dom34 and its binding partner Hbs1. In contrast, 25S NRD is translation independent and involves the E3 ligase components Rtt101 and Mms1. These pathways were identified using specifically engineered mutant rRNAs, but NRD may normally function to remove accumulated nonfunctional rRNAs that can arise as a result of genotoxic stress such as UV radiation. Understanding rRNA damage and decay is of special importance because rRNA makes up to 90% of the total RNA in S. cerevisiae. Therefore, we are interested in determining the effect of ultraviolet (UV) radiation on NRD to better understand how the 18S and 25S NRD pathways affect cell survival. We hypothesize that by removing damaged rRNAs, NRD can increase cell survival under certain stress conditions. To investigate the effect of UV radiation on NRD function, we transformed BY4741 S. cerevisiae with various rRNA expression plasmids. These plasmids encode either functional or nonfunctional versions of the 18S and 25S rRNAs. The plasmid‐derived rRNAs also contain short, unique sequence tags that allow specific detection of these rRNAs in the presence of total cellular rRNA. The transformed cells were exposed to increasing amounts of UV radiation and cell growth after exposure was monitored in both liquid and solid media. Currently, we are determining relative expression levels of WT and nonfunctional rRNAs using an RT‐qPCR assay. Furthermore, we are continuing these same experiments in NRD‐deficient yeast strains. This work may ultimately help elucidate the role of NRD in cellular recovery from UV damage and contribute to a better understanding of the NRD pathway.Support or Funding InformationThis work is supported by the Howard Hughes Medical Institute.