A pure polypeptide containing an amino acid sequence at least 70% identical to SEQ ID NO:7, 8, or 9. The polypeptide regulates expression of a gene in a cell. Also disclosed is an isolated nucleic acid characterized in that it hybridizes under stringent conditions to SEQ ID NO:1, 2, or 3, or a complementary sequence thereof. Also within the scope of the invention are a transformed cell or a transgenic plant containing such a nucleic acid and a method of identifying a compound that modulates the activity of the polypeptide.