Helix-turn-helix, Psq-like The psq-type domain is a DNA-binding, helix-turn-helix (HTH) motif found in four copies in the <taxon tax_id="7227">Drosophila melanogaster</taxon> (Fruit fly) pipsqueak (psq) protein. In psq this domain binds to the GAGA sequence, and is essential for sequence-specific targeting of a polycomb group protein complex. Proteins of the Pipsqueak family occur in vertebrates, insects, nematodes, and fungi. Three subgroups of the family have been described, BTB, E93 and CENP-B, where each group displays a different domain organisation [<cite idref="PUB00014772"/>]. The BTB (Broad-complex, Tramtrack, Bric-a-brac) subfamily are transcriptional regulators that contain a BTB protein-protein interaction domain (<db_xref db="INTERPRO" dbkey="IPR000210"/>) near the N-terminal, and the psq-type HTH domain near the C-terminal [<cite idref="PUB00014768"/>]. The E93 subfamily contain a psq-type HTH domain at varying positions, E93 being a Drosophila cell death regulating protein. The CENP-B (human centromere protein B) subfamily contain a psq-type HTH domain (<db_xref db="INTERPRO" dbkey="IPR006695"/>) near the N-terminal, often with a dimerisation domain near the C-terminal; this group includes fungal transposases that lack part of the psq domain.