passages.id: split_8_test_2552_passage
passages.type: progene_text
passages.text: Surface - exposed residues of helix 3 and helix 6 , the recognition helices of the dual HTH motifs , are important to DNA binding and transcription activation ; however , substitutions of residues predicted from the MarA - mar crystal structure to make contact with the sugar - phosphate backbone are more detrimental to DNA binding than mutations predicted to make base - specific contacts .