in summary , we have developed a novel dna binding motif consisting of two 
 dna binding fragments of natural tfs connected via an at - hook 
 linker , which allows the selective recognition of designed , extended dna sequences 
 ( up to 13 bp ) .
the success of this design relies on the ability of the at - hook 
 moiety to act as a bidentate minor groove - anchoring device that delivers the dna 
 binding tf fragments to appropriate positions for insertion in their respective 
 major grooves .
the peptidic nature of the at - hook allowed an easy installation of 
 each of the dna binding peptides at the c- and n - terminus of the anchor .
the construct represents the first demonstration of an engineered synthetic 
 dna binder that reaches two consecutive major grooves across the minor groove . the 
 tripartite ( major  minor  major groove ) recognition introduces a novel 
 dna binding motif that lacks a natural counterpart .
this approach promises to be 
 applicable to other dna binding tf fragments addressing different sites , and 
 introduces a novel way of targeting specific and long dna sequences .
  electronic supplementary information ( esi ) available : 
 peptide synthesis , full experimental procedures and analytical data of the peptides 
 and products obtained .
 we report the rational design of a dna - binding peptide construct composed 
 of the dna - contacting regions of two transcription factors ( gcn4 and gaga ) 
 linked through an at - hook dna anchor . the resulting chimera , which represents a 
 new , non - natural dna binding motif , binds with high affinity and selectivity to 
 a long composite sequence of 13 base pairs ( tcat - aatt - gagag ) . 