The operon model of the regulation of gene expression in bacteria was proposed by François Jacob and Jacques Monod in 1961. This groundbreaking model was based on their studies of the lac operon in Escherichia coli (E. coli), which demonstrated how genes involved in lactose metabolism are coordinately regulated. Jacob and Monod's work laid the foundation for understanding gene regulation and provided insights into the principles of transcriptional control in prokaryotes.