Allostery and the lac Operon.

The ability to regulate gene expression is essential for controlling metabolic events in a cell. Proteins that function like molecular switches respond to fluctuations in the environment to maintain homeostasis. The operon model, proposed by Jacob and Monod, provides a cogent depiction for how gene expression is regulated. A molecular mechanism for the regulation followed shortly with the theory for allosteric transition. Over the past half-century, the details of the lac operon and the allosteric model have been tested using genetic, biochemical, and structural techniques. Remarkably, the principles originally put forward 50 years ago remain essentially unchanged. Models for the operon and the theory of allosteric transitions are two of the most profound discoveries of molecular biology.