THE SOLUTION STRUCTURE OF A SPECIFIC GAGA FACTOR-DNA COMPLEX REVEALS A MODULAR BINDING MODE

The structure of a complex between the DNA binding domain of the GAGA factor (GAGA-DBD) and an oligonucleotide containing its GAGAG consensu s binding site has been determined by nuclear magnetic resonance spect roscopy. The GAGA-DBD comprises a single classical Cys(2)-His(2), zinc finger core, and an N-terminal extension containing two highly basic regions, BR1 and BR2. The zinc: finger core binds in the major groove and recognizes the first three GAG bases of the consensus in a manner similar to that seen in other classical zinc finger-DNA complexes. Unl ike the tatter, which require tandem zinc finger repeats with a minimu m of two units for high affinity binding, the GAGA-DBD makes use of on ly a single finger complemented by BR1 and BR2. BR2 forms a helix that interacts in the major groove recognizing the last G of the consensus , while BR1. wraps around the DNA in the minor groove and recognizes t he A in the fourth position of the consensus. The implications of the structure of the GAGA-DBD-DNA complex for chromatin remodelling are di scussed.