Researchers are eyeing another step in the virus-building pipeline: the generation of virus genes, before they are packaged into their protein capsules. Carlos Bustamante, a biophysicist at the University of California, Berkeley, is set on sabotaging a protein called polymerase, which copies the coronavirus's genome. "We are playing tug of war," Dr. Bustamante said. "Every time it moves, it has to pull us." The hope, he said, is to understand the tug well enough to design a drug that blocks the RNA-copying process.