The ARID (A–T Rich Interaction Domain) is a helix–turn–helix motif-based DNA-binding domain, conserved in all eukaryotes and diagnostic of a family that comprises 15 distinct human proteins. ARID proteins, although diverse in function, all appear to play important roles in development, tissue-specific gene expression and cell growth regulation [reviewed in (1,2)]. The ARID consensus sequence, which spans about 100 residues, was first identified as a DNA-binding domain in the mouse B cell-specific transcription factor, Bright (3), and in the Dead ringer protein (Dri) of Drosophila melanogaster (4). Dri and Bright were each isolated in searches designed to detect proteins binding selectively to AT-rich sequences. Recognition of the Bright/Dri consensus defined the parameters of a new DNA-binding domain, and the properties of Bright and Dri inspired its name. MRF-1 and MRF2, which bind the CMV enhancer and repress its activity, are also ARID-containing proteins that bind selectively to AT-rich sites (5,6).
