The mechanism by which phytohormones, like abscisic acid (ABA), regulate gene expression is unknown. An activity in nuclear extracts that interacts with the ABA response element (ABRE) from the 5′ regulatory region of the wheat Em gene was identified. A complementary DNA clone was isolated whose product is a DNA binding protein (EmBP-1) that interacts specifically with an 8-base pair (bp) sequence (CACGTGGC) in the ABRE. A 2-bp mutation in this sequence prevented binding of EmBP-1. The same mutation reduced the ability of the ABRE to confer ABA responsiveness on a viral promoter in a transient assay. The 8-bp EmBP-1 target sequence was found to be conserved in several other ABA-responsive promoters and in promoters from plants that respond to signals other than ABA. Similar sequences are found in promoters from mammals, yeast, and in the major late promoter of adenovirus. The deduced amino acid sequence of EmBP-1 contains conserved basic and leucine zipper domains found in transcription factors in plants, yeast, and mammals. EmBP-1 may be a member of a highly conserved family of proteins that recognize a core sequence found in the regulatory regions of various genes that are integrated into a number of different response pathways.
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