Regulation of the l-Arabinose Operon BAD in Vitro

A DNA-directed cell-free system to study the l-arabinose BAD operon has been further developed so that the rate of synthesis of enzymes coded for by the structural genes in the operon in vitro is about 5% the in vivo rate. l-Arabinose isomerase and l-ribulokinase, the products of the araA and araB genes, are synthesized at the same rate, demonstrating that the operon is coordinately expressed in vitro. The system is completely dependent upon araC protein which can be supplied either by synthesis in vitro from an araC+ DNA template or by the addition of araC protein extracted from whole cells. The properties in the in vitro system of araC protein from either source suggests that the two products are similar if not identical. Both the repressor and activator forms of the araC protein are demonstrable in vitro using the appropriate templates confirming the essential aspects of the model for gene regulation of this operon.