THE TRP REPRESSOR, A LIGAND-ACTIVATED REGULATORY PROTEIN

This chapter discusses the role of Trp repressor as a ligand-activated regulatory protein. The Trp repressor (protein) of Escherichia coli is one of the most exhaustively studied DNA-binding regulatory macromolecules. Its physiological role is to reduce or eliminate transcription from certain regulatable promoters through the formation of RNA-polymerase-preemptive non covalent complexes between protein and DNA. The structure–function analyses carried out on the Trp repressor place this system in the top rank in terms of the breadth and detail of the information that is available. The chapter reviews the existing body of knowledge about the Trp repressor with the goal of distinguishing general structure–function principles, as well as specific features that might also apply to other amino-acid-activated proteins able to form complexes with duplex DNA. The Trp repressor engages appropriate operator targets within DNA only if the protein has first undergone a tryptophan-mediated conformational change. The geometry of several complexes involving the Trp repressor is now well understood at the atomic level from X-ray crystallographic comparisons of liganded and unliganded species and from the analysis of a crystalline Trp-holorepressor-operator complex. The crystallographic results have recently been obtained. © 1992, Academic Press Inc.