Auxin-response factors (ARFs) bind with specificity to TGTCTC auxin-response elements(AuxREs), which are found in promoters of primary/early auxin-response genes. The ARF1 protein contains an amino-terminal DNA-binding domain (DBD), which has some sequence similarity to a carboxyl-terminal B3 domain found in the maize transcription factor VIVIPAROUS 1 (VP1) and its relatives. ARF1 contains a carboxyl-terminal domain (CTD) related to motifs III and IV found in the CTDs of Aux/IAA proteins, which are short-lived nuclear proteins encoded by a family of primary/early auxin-response genes. The CTDs in ARF1 and Aux/IAA proteins facilitate dimerization among the members of both ARF and Aux/IAA protein families. The prebound transcription factors facilitate activated transcription when auxin levels are elevated or when ARF activators are overexpressed in transfected protoplasts. The results also suggest that ARF CTDs facilitate interactions between ARF activators that are not bound to DNA and transcription factors (e.g., ARFs) that are bound to AuxREs to further enhance transcription.