In a cell free system , binding of a DNA fragment ( GCGTGAGCGCTCACAGGTCAATTCG ) and mutant __SP__ __NODE__ protein ( C terminal truncation 250 End with its DNA binding domain retained ) is greater than binding of a DNA fragment ( GCGTGAGCGCTCACAGGTCAATTCG ) and mutant __SP__ __NODE__ protein ( C terminal truncation 225 End with its DNA binding domain retained ) .