(490.5) Increased Oxidation From Glucose Limiting Conditions or SOD Deletions Result in Activation of No-Go Decay and Subsequent P-body Assembly

Poster Board Number: A102

Scott Segal (Winona State University), Emily Cianflone (Winona State University), Anna Jorgensen (Winona State University), Gretchen McManus (Winona State University), Kyle Rolin (Winona State University)

The budding yeast, Saccharomyces cerevisiae preferentially metabolizes glucose anaerobically when it is abundant.   However, as glucose becomes depleted, yeast will enter diauxic shift.  Under this condition, growth will slow, and glucose becomes metabolized aerobically.  Upregulation of aerobic glucose metabolism ultimately leads to the increase of intracellular reactive oxygen species (ROS).  The increase of ROS can lead to oxidation of nucleic acids through formation of 8-oxoguanine bases (8-oxoG).  In mRNA the presence of 8-oxoG can elicit ribosome stalls, resulting in translational shutdown and the activation of the no-go mRNA quality control pathway.  No-go decay is mediated by the proteins Hbs1p and Dom34p, which act to remove stalled ribosomes, and will promote cleavage of the mRNA at the stall site.  The remaining 5’ fragment is subject to 3’-5’ decay by the cytoplasmic exosome, while the 3’ fragment is degraded 5’-3’ by exonuclease Xrn1p in P-bodies, which are sites of mRNA degradation.

Upon growing yeast into diauxic shift, an increase in P-body assembly was observed.  P-bodies contain mRNA decay enzymes and are sites where nontranslating mRNA will localize to be degraded. This observed increase in P-body assembly appears to be due to an upregulation of no-go Decay, as P-body assembly is reduced in strains lacking either Dom34p or Hbs1p.  Upon exposure to the antioxidant quercetin during diauxic shift, P-body assembly is abrogated showing that generation of ROS is responsible for the activation of no-go decay and subsequent P-body assembly.  The same result is phenocopied by exposing yeast to glucose limiting conditions (0.5% glucose).  As expected with the increased oxidation from glucose limiting conditions, global translation is also reduced.  Interestingly, strains lacking either Sod1p or Sod2p, also show a reduction in global translation, along with an upregulation of no-go decay and P-body assembly.   These data suggest that physiological stresses that lead to an increase in ROS, which can damage mRNA leading to activation of No-Go Decay and subsequent P-body assembly.