Determination of genetic interaction networks (GINs) surrounding drug targets identifies buffering genes and provides molecular insight into drug response in individuals. Here we used backcross methodology to create Saccharomyces cerevisiae deletion libraries in three genetic backgrounds resistant to statins, which are additional to the statin-sensitive S288C deletion library that has provided much of what is known about GINs in eukaryotes. Whole genome sequencing and linkage group analysis confirmed the genomic authenticity of the new deletion libraries. Statin response was probed by drug-gene interactions with atorvastatin and cerivastatin treatments, as well as gene-gene interactions with the statin target HMG1 and HMG2 genes or the sterol homeostatic ARV1 gene. The 20 GINs generated from these interactions were not conserved by function or topology across the four genetic backgrounds. Centrality measures and hierarchical agglomerative clustering identified master regulators that if removed collapsed the networks. Community structure distinguished a characteristic early secretory pathway pattern of gene usage in each genetic background. ER stress in statin-resistant backgrounds was buffered by protein folding genes, which was confirmed by reduced activation of the unfolded protein response in statinresistant backgrounds relative to the statin-sensitive S288C background. These network analyses of new gene deletion libraries provide insight into the complexity of GINs underlying individual drug response.Statins target HMG-CoA-reductase and are amongst the most prescribed of all therapeutic drugs 19 . However, they have significant side-effects in some individuals such as muscular myopathies 20,21 and exhibit individual variation in clinical efficacy 22 . Atorvastatin and cerivastatin are two cholesterol-lowering drugs that have the same target, HMG-CoA reductase (encoded by HMGCR in humans and the orthologous paralogues HMG1 and HMG2 in yeast), but cerivastatin is no longer FDA-approved owing to adverse side effects, suggesting that analysis of GINs in response to these drugs in different individual genetic backgrounds could be critical to fully understanding the mechanisms of these drugs. The statin drug target and sterol pathways are conserved from yeast to humans 23 , the HMG1/2 deletion has been used as a genetic mimic of statin treatment 24,25 , chemical genomic 4 analyses in yeast elucidated the cellular response to statins 26 , and genome-wide analyses in yeast identified GIs with the HMG1/2 statin drug target 13 .Deletion libraries in the yeast S288C background used in synthetic genetic array (SGA) and chemical genetic analyses have provided much of what is known about GINs in eukaryotes 10,13,27,28 . In this paper we extended the scope of the S288C literature by creating three new deletion libraries in three additional yeast strains of different genetic backgrounds. We identified GIs with atorvastatin, cerivastatin, and statin target HMG1, its functional paralog HMG2, and the sterol homeostatic ARV1 gen...