Zinc fingers (ZnFs) are among the most common of all protein domains. They have traditionally been regarded as sequence-specific DNA-binding motifs. However it has also become apparent that many ZnFs mediate specific protein-protein interactions. Transcriptional cofactors of the Friend of GATA (FOG) family are diverse in sequence but their individual ZnF regions share considerable homology. They contain either eight or nine ZnFs that are related to the classical CCHH ZnFs (which have a conserved C-X(2,5)-C-X(12)-H-X(2,5)-H sequence). Several of the fingers in each FOG protein, however, have an altered consensus sequence in which the final zinc binding histidine is replaced with a cysteine. Interestingly, it is only these variant CCHC ZbFs that mediate interactions with GATA N-terminal zinc fingers (NFs) [1,2,3,4,5].

The FOG-type CCHC zinc finger comprises a short β hairpin followed by an α helix (see <PDB:1FU9>). It resembles classical CCHH fingers in structure. The only notable difference is a short extended portion of the polypeptide backbone before the fourth zinc ligand. Two of the residues implicated in GATA binding are located on the extended portion of the backbone, immediately preceding the final cysteine. Thus, the CCHC topology appears to play a key role in facilitating the interaction. The residues that are implicated in GATA binding are largely conserved across FOG family CCHC ZnFs, although three of the residues that affect the binding affinity show some variation [1,2].

Some proteins known to contain a FOG-type CCHC zinc finger are listed below:

• Vertebrate Friend of GATA-1 (FOG-1), a zinc finger protein that interacts physically with the erythroid DNA-binding protein GATA-1 and modulates its transcriptional activity.
• Mammalian FOG-2, associates with GATA-1 and other mammalian GATA factors.
• Drosophila melanogaster U-shaped (Ush), interacts with the GATA factors Pannier and Serpent to control development in the fly.

The profile we developed covers the entire FOG-type CCHC zinc finger.