 Jacob and Monod’s view was grounded on their pioneering work on bacterial gene expression (1961a, 1961b). Their key result, the operon model, explains how gene expression in E. coli bacteria is regulated by environmental signals. Briefly, the model represents interactions among various components: protein-encoding DNA sequences, regulatory DNA sequences, the “operator region” of DNA located near the start of protein-encoding genes, repressor protein, and small molecules (e.g., allolactose). If a repressor binds the operator region, this blocks protein synthesis at nearby coding sequences. Small molecules like allolactose bind the repressor, inhibiting its inhibition, so the protein-encoding genes associated with the “de-repressed” operator are expressed. Those genes encode enzymes involved in metabolizing the small molecules, neatly closing the regulatory loop. Jacob and Monod singled out DNA as the controlling molecule of this regulatory system. Furthermore, as Michael Morange (2000) discusses, they extrapolated the E. coli operon model to gene regulation in general, positing that all organismal development is controlled by a small set of regulatory genes.