Cryo-electron microscopy (cryo-EM) structure of beta-galactosidase. With cryo-EM, scientists can view in near-atomic detail the architecture of a metabolic enzyme bound to a drug that blocks its activity. This advance provides a new path for solving molecular structures during drug development. Beta-galactosidase is commonly used in molecular biology as a reporter marker to monitor gene expression. It also exhibits a phenomenon called alpha-complementation which forms the basis for the blue/white screening of recombinant clones.