A novel DNA-binding motif in MarA: the first structure for an AraC family transcriptional activator.

A crystal structure for a member of the AraC prokaryotic transcriptional activator family, MarA, in complex with its cognate DNA-binding site is described. MarA consists of two similar subdomains, each containing a helix-turn-helix DNA-binding motif. The two recognition helices of the motifs are inserted into adjacent major groove segments on the same face of the DNA but are separated by only 27 A thereby bending the DNA by approximately 35 degrees. Extensive interactions between the recognition helices and the DNA major groove provide the sequence specificity.