A C4HC3 zinc finger motif

Abstract

Metal-binding cysteine and histidine residues are often used to stabilise a protein fold through coordination of zinc ions. These zinc fingers are either involved in nucleic acid binding (TFIIIA, GAL4, nuclear receptors, retroviral gag...) or in yet unidentified biochemical functions (LIM and RING domains). The latter characterized by a unique histidine residue in the zinc binding motif (C2HC5 and C3HC4 for the LIM and RING respectively) may constitute protein/protein interaction interfaces. We have identified a new C4HC3 motif in a variety of proteins including the Drosophila trithorax and its human homologue ALL-1 involved in oncogenic translocations in acute leukaemias. This domain, for which we propose the name TTC (for trithorax consensus) is found in many transcriptional regulators or DNA-binding proteins. Interestingly, TTC was found in several bromodomain containing transcriptional adaptors including the E1A-binding p300 and the CREB-binding CBP proteins. In CBP, this domain does not appear to be involved in DNA, CREB or TFIIB binding. In the chromosomal translocations that involve the 11q23 locus, the C-terminal end of ALL-1 (which contains 4 TTC fingers) is constantly lost. The absence of these motifs in the fusion genes may relate to their leukemogenic potential.