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 transcription al activator family, MarA, in complex with its cognate DNA-binding sit e is described. MarA consists of two similar subdomains, each containi ng a helix-turn-helix DNA-binding motif. The two recognition helices o f the motifs are inserted into adjacent major groove segments on the s ame face of the DNA but are separated by only 27 Angstrom thereby bend ing the DNA by approximate to 35 degrees. Extensive interactions betwe en the recognition helices and the DNA major groove provide the sequen ce specificity.