The THAP domain of THAP1 is a large C2CH module with zinc-dependent sequence-specific DNA-binding activity

We have recently described an evolutionarily conserved protein motif, designated the THAP domain, which defines a previously uncharacterized family of cellular factors (THAP proteins). The THAP domain exhibits similarities to the site-specific DNA-binding domain of Drosophila P element transposase, including a putative metal-coordinating C2CH signature (CX(2-4)CX(35-53)CX(2)H). In this article, we report a comprehensive list of approximately 100 distinct THAP proteins in model animal organisms, including human nuclear proapoptotic factors THAP1 and DAP4/THAP0, transcriptional repressor THAP7, zebrafish orthologue of cell cycle regulator E2F6, and Caenorhabditis elegans chromatin-associated protein HIM-17 and cell-cycle regulators LIN-36 and LIN-15B. In addition, we demonstrate the biochemical function of the THAP domain as a zinc-dependent sequence-specific DNA-binding domain belonging to the zinc-finger superfamily. In vitro binding-site selection allowed us to identify an 11-nucleotide consensus DNA-binding sequence specifically recognized by the THAP domain of human THAP1. Mutations of single nucleotide positions in this sequence abrogated THAP-domain binding. Experiments with the zinc chelator 1,10-o-phenanthroline revealed that the THAP domain is a zinc-dependent DNA-binding domain. Site-directed mutagenesis of single cysteine or histidine residues supported a role for the C2CH motif in zinc coordination and DNA-binding activity. The four other conserved residues (P, W, F, and P), which define the THAP consensus sequence, were also found to be required for DNA binding. Together with previous genetic data obtained in C. elegans, our results suggest that cellular THAP proteins may function as zinc-dependent sequence-specific DNA-binding factors with roles in proliferation, apoptosis, cell cycle, chromosome segregation, chromatin modification, and transcriptional regulation.