THE LEUCINE-RESPONSIVE REGULATORY PROTEIN (LRP) FROM ESCHERICHIA-COLI- STOICHIOMETRY AND MINIMAL REQUIREMENTS FOR BINDING TO DNA

Lrp (Leucine-responsive regulatory protein) regulates the expression o f a number of operons in Escherichia coli, A recent study of DNA seque nces recognized by Lrp established the consensus as a 15-bp sequence, YAGHA-WATTWTDCTR (Y = C/T, H = ''not G,'' W = A/T, D = ''not C,'' R = A/G) (Cui, Y., Wang, Q,, Stormo, G, D,, and Calvo, J, M, (1995) J, Bac teriol, 177, 4872-4880). Here we report the stoichiometry of Lrp bindi ng (an Lrp dimer binds to a single binding site) and studies that defi ne the minimal length of DNA required for binding, A double-stranded 1 5 mer having a sequence that closely matches the consensus does not sh ow measurable binding to Lrp, One or two base pairs of DNA flanking ea ch end are not sufficient for binding, but constructs having 3-5 addit ional base pairs (21 mer) show relatively strong binding, Single-stran ded flanking DNA also contributes to strong binding, The extent of the contribution to binding is dependent upon whether the single strand i s on the left or right of the double stranded region and whether the p olarity of the single-stranded DNA is 5' to 3' or 3' to 5'.