The single Cys2-His2 zinc finger domain of the GAGA protein flanked by basic residues is sufficient for high-affinity specific DNA binding

Specific DNA binding to the core consensus site GAGAGAG has been shown with an 82-residue peptide (residues 310-391) taken from the Drosophila transcription factor GAGA. Using a series of deletion mutants, it was demonstrated that the minimal domain required for specific binding (residues 310-372) includes a single zinc finger of the Cys2-His2 family and a stretch of basic amino acids located on the N-terminal end of the zinc finger. In gel retardation assays, the specific binding seen with either the peptide or the whole protein is zinc dependent and corresponds to a dissociation constant of ≃5 x 10-9 M for the purified peptide. It has previously been thought that a single zinc finger of the Cys2-His2 family is incapable of specific, high-affinity binding to DNA. The combination of an N-terminal basic region with a single Cys2-His2 zinc finger in the GAGA protein can thus he viewed as a novel DNA binding domain. This raises the possibility that other proteins carrying only one Cys2-His2 finger are also capable of high-affinity specific binding to DNA

The Arabidopsis SUPERMAN protein is able to specifically bind DNA through its single Cys2-His2 zinc finger motif

The Arabidopsis SUPERMAN (SUP) gene has been shown to be important in maintaining the boundary between stamens and carpels, and is presumed to act by regulating cell proliferation. In this work, we show that the SUP protein, which contains a single Cys2-His2 zinc finger domain including the QALGGH sequence, highly conserved in the plant zinc finger proteins, binds DNA. Using a series of deletion mutants, it was determined that the minimal domain required for specific DNA binding (residues 15-78) includes the single zinc finger and two basic regions located on either side of this motif. Furthermore, amino acid substitutions in the zinc finger or in the basic regions, including a mutation that knocks out the function of the SUP protein in vivo (glycine 63 to aspartate), have been found to abolish the activity of the SUP DNA-binding domain. These results strongly suggest that the SUP protein functions in vivo by acting as a DNA-binding protein, likely involved in transcriptional regulation. The association of both an N-terminal and a C-terminal basic region with a single Cys2-His2 zinc finger represents a novel DNA-binding motif suggesting that the mechanism of DNA recognition adopted by the SUP protein is different from that described so far in other zinc finger proteins

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 consensus binding site has been determined by nuclear magnetic resonance spectroscopy. The GAGA-DBD comprises a single classical Cys2-His2 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. Unlike the latter, which require tandem zinc finger repeats with a minimum of two units for high affinity binding, the GAGA-DBD makes use of only 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 the A in the fourth position of the consensus. The implications of the structure of the GAGA-DBD-DNA complex for chromatin remodelling are discussed