Yhk8 as a genomic modifier of copper susceptibility in yeast

Copper is essential for life as an enzymatic cofactor and antioxidant participant, but in excess, it is toxic to all living organisms, including yeast. Because this toxicity varies by genetic background, we investigated the underlying modifier genes using a panel of four genetically diverse strains—Sake (SA), North American (NA), West African (WA), and Wine/European (WE)—and their segregants. Copper sulfate (CuSO 4 ) susceptibility, quantified by the maximum growth rate (µMax), was strain-dependent, with resistance decreasing in the order SA > WE > WA > NA. Furthermore, cellular growth was inversely correlated with intracellular superoxide levels measured via dihydroethidium staining. By analyzing µMax in 96 segregants from an SA x NA cross exposed to CuSO 4 , we performed quantitative trait locus (QTL) mapping and prioritized 17 candidate modifiers. Functional validation in deletion strains identified Yhk8—a putative drug/proton antiporter functionally similar to the human SLC47A1 gene—as a novel copper susceptibility gene, with its deletion resulting in impaired growth and elevated superoxide levels. Together, these findings establish Yhk8 as a key genetic modifier of copper response in yeast.