LRP, A MAJOR REGULATORY PROTEIN IN ESCHERICHIA-COLI, BENDS DNA AND CAN ORGANIZE THE ASSEMBLY OF A HIGHER-ORDER NUCLEOPROTEIN STRUCTURE

Lrp (Leucine-responsive regulatory protein) is a global regulatory pro tein that controls the expression of many operons in Escherichia coli. One of those operons, ilvIH, contains six Lrp binding sites located w ithin a several hundred base pair region upstream of the promoter regi on. Analysis of the binding of Lrp to a set of circularly permuted DNA fragments from this region indicates that Lrp induces DNA bending. Th e results of DNase I footprinting experiments suggest that Lrp binding to this region facilitates the formation of a higher-order nucleoprot ein structure. To define more precisely the degree of bending associat ed with Lrp binding, one or two binding sites were separately cloned i nto a pBend vector and analyzed. Lrp induced a bend of approximately 5 2-degrees upon binding to a single binding site, and the angle of bend ing is increased to at least 135-degrees when Lrp binds to two adjacen t sites. Lrp-induced DNA bending, and a natural sequence-directed bend that exists within ilvIH DNA, may be architectural elements that faci litate the assembly of a nucleoprotein complex.