Crystal structure of the lactose operon repressor and its complexes with DNA and inducer

In 1961 Francois Jacob and Jacques Monod published a landmark paper in which they were the first to predict the existence of some repressor molecule which would be responsible for gene regulation. A key component of the model is the lac repressor molecule which binds to a specific sites on the gene and functions as a molecular switch in response to small metabolites or inducer molecules. This thesis deals with work to understand how transcription or protein expression is regulated at the molecular level. The three-dimensional structures of the intact lac repressor, the lac repressor bound to the non-metabolizable inducer, isopropyl-$\beta$- sc D-1-thiogalactoside (IPTG), and the lac repressor complexed with a 21-base pair symmetric fragment of DNA have been solved by X-ray crystallography. These structures provide not only the framework for interpreting a wealth of biochemical and genetic information but also suggest an explicit model for how the tetrameric form of the lac repressor interacts with DNA and functions synergistically with the other molecules to regulate gene expression