24 Regulation of the L-Arabinose Catabolic Operon araBAD

Abstract

OVERVIEW
Regulation of the L-arabinose operon began as an exercise in genetics in Escherichia coli many years ago. This led to the discovery of positive regulation, which, in turn, awakened researchers to the possibility of many modes of gene regulation, as are now known. DNA looping was first discovered and demonstrated in the arabinose operon. In this chapter, both the regulation of the arabinose operon and DNA looping are discussed. The discussion includes biological and physical reasons that DNA looping is sensible. Yet to be learned in the system is how the protein can possess the flexibility necessary to participate in the known DNA-binding structures, the structure of the protein, and the actual mechanism of transcription activation.

INTRODUCTION
The Arabinose Operon
Genes of the L-arabinose operon of E. coli enable the cells to take up and catabolize the pentose sugar L-arabinose. Arabinose is found naturally in polysaccharides of plant cell walls. Since humans cannot take up or catabolize arabinose, a meal with vegetables provides our guests (E. coli) with a free lunch. Likely then, the mechanisms for regulation of the arabinose operons in E. coli reflect the value of being able to respond rapidly to the periodic pulses of arabinose seen by the bacterium. The regulatory protein, AraC, of the arabinose system senses the presence of arabinose and induces synthesis of proteins that transport arabinose into cells and then catabolize the intracellular arabinose.

The arabinose catabolic operon consists of three genes that code for the enzymes necessary to convert L-arabinose...