Updated publication reference for DOI(s): 10.1126/science.abe9403. Abstract: The COVID-19 (Coronavirus disease-2019) pandemic, caused by the SARS-CoV-2 coronavirus, has highlighted emergent viruses as significant threats to public health and the global economy. SARS-CoV-2 is closely related to the more lethal but less transmissible coronaviruses SARS-CoV-1 and MERS-CoV. Here, we have carried out comparative viral-human protein-protein interaction and viral protein localization analysis for all three viruses. We find that proteins often do not change localization across viruses but their sequence divergence dictates differences in host interactions. Functional genetic screening identified host factors that functionally impinge on coronavirus proliferation, including Tom70, a mitochondrial chaperone protein that interacts with both SARS-CoV-1 and SARS-CoV-2 Orf9b, an interaction we structurally characterized using cryoEM. Combining genetically validated host factors with both COVID-19 patient genetic data and medical billing records identified important molecular mechanisms (IL-17 regulation) and drug treatments (sigma-1 receptor ligands) that merit further molecular and clinical study.