The precise function of all the human ARID proteins is not known. Members of the AT-specific ARID3 and ARID5 subfamilies are sequence-specific transcription factors with recognized promoter targeting functions and important roles in development and differentiation (3,4,5,38–40). Among the sequence-non-specific ARID proteins, several appear to participate in general transcription and chromatin remodeling functions. ARID1A and ARID1B are mutually alternative members of human SWI/SNF-related complexes (20,41,42) and ARID1A (p270) is implicated in the tumor suppressor activity of the complexes (43). Human ARID2 is uncharacterized, but the Drosophila ortholog of ARID2 is a member of a SWI/SNF-like complex (22). ARID4A and ARID4B can associate with the mSIN3-histone deacetylase complex (19,25). Members of the JARID1 and JARID2 subfamilies show transcription activation and/or repression functions (26,27,34). To date, only the Dri and Bright (ARID3A) ARIDs have actually been shown to be required for the physiological function of their cognate proteins (44,45). The ARID of the S.cerevisieae protein SWI1 appears dispensable for complementation of the SWI1 phenotype (46), but transient reporter assays suggest the ARID is required for a transactivation function in human ARID1B (41). More physiological experiments are needed.
