Specific beta-sheet interactions

The dramatic success of structural studies of helix-turn-helix repressors and their complexes with DNA has overshadowed the possibility of the use of beta-strands for sequence recognition by specific DNA- or RNA-binding proteins. The structure determinations of Met and Arc repressors, which use two-stranded antiparallel beta-ribbons to insert into the major groove of B-DNA, and make sequence-specific contacts to bases, may have revealed a major new binding motif. The sequence-specific DNA-binding proteins IHF and TF1, related to the non-specific HU, whose structure has been refined to high resolution, demonstrate a different binding mode, apparently recognizing DNA sequence from the minor groove. Related arrangements had been proposed in the 1970s on the basis of model building studies.