In molecular biology, the ARID domain (AT-rich interaction domain; also known as BRIGHT (B-cell Regulator of Ig Heavy chain Transcription) domain)) is a protein domain that binds to DNA. ARID domain-containing proteins are found in fungi, plants and invertebrate and vertebrate metazoans. ARID-encoding genes are involved in a variety of biological processes including embryonic development, cell lineage gene regulation and cell cycle control. Although the specific roles of this domain and of ARID-containing proteins in transcriptional regulation are yet to be elucidated, they include both positive and negative transcriptional regulation and a likely involvement in the modification of chromatin structure. The basic structure of the ARID domain appears to be a series of six alpha-helices sepa