Abstract 2124 The yeast Mkt1/Pbp1 complex promotes adaptive responses to respiratory growth

Mkt1 (Maintenance of K2 Killer Toxin 1) is a poorly understood protein belonging to the Rad2/XPG family of DNA repair enzymes. Quantitative trait locus studies have shown that a single Mkt1 amino acid polymorphism (Mkt1-G30D) underlies variation seen across many phenotypes in laboratory S. cerevisiae strains. These studies have suggested an important role for Mkt1 in promoting mitochondrial function, but this has not been thoroughly tested. Mkt1 is thought to form a complex with yeast ataxin-2, or Pbp1 (polyA binding protein-binding protein 1), which we have shown is required during respiratory growth for the translation of nuclear-encoded mitochondrial proteins regulated by Puf3 and for TORC1-dependent induction of autophagy. We used CEN.PK yeast which naturally have the wild-type Mkt1-G30 allele to find that Mkt1 is required like Pbp1 in Puf3-target mRNA translation and autophagy. Notably, expression of the loss-of-function Mkt1-D30 allele in CEN.PK yeast led to reduced Mkt1 and Pbp1 protein levels and disruption of both Puf3-target protein expression and autophagy. Furthermore, we observed S288C yeast which have evolved the Mkt1-D30 allele are deficient in Mkt1/Pbp1 complex abundance, Puf3-target mRNA translation, and autophagy, and all of these defects were rescued by expression of the wild-type Mkt1-G30 allele. Thus, Mkt1 and Pbp1 function in a complex to promote vital processes during respiratory growth, and the Mkt1-G30D polymorphism may represent an adaptation by 20th century yeast to limit mitochondrial function for survival in artificial, glucose-rich laboratory environments. This research project is funded by the Howard Hughes Medical Institute and the National Institutes of Neurological Disorders and Stroke.