Transcriptional activator that binds to the DNA specific sequence 5'-TGAGTCA-3' found in seed storage protein gene promoters. Involved in the endosperm-specific regulation of storage protein genes (PubMed:15685292). Can activate the expression of genes encoding for the seed storage proteins glutelin, prolamin, globulin and the allergen RAG1. Functions synergistically with DOF3/RPBF to positively regulate quantitatively many seed storage protein genes (PubMed:16798940, PubMed:19473328). Functions synergistically with DOF3/RPBF to positively regulate some metabolic enzymes, such as alanine aminotransferase and pyruvate phosphate dikinase, that are expressed in developing seeds (PubMed:16798940). Functions synergistically with DOF3/RPBF to positively regulate genes that are key players in the development of aleurone layers (PubMed:19473328). Functions synergistically with DOF3/RPBF to positively regulate the glutelin GLUD-1 gene in endosperm of developing seeds (PubMed:18980953). Can activate the expression of the bifunctional lysine-degrading enzyme, lysine ketoglutarate reductase/saccharopine dehydrogenase (LKR/SDH), one of the key regulators determining free lysine content in plants (PubMed:21037241). Functions as a key regulator of starch synthesis in seeds, by direct binding to the promoters of starch-synthesizing genes, such as AGPL3, WAXXY and SBE1 (PubMed:23846875). Homodimer. Forms heterodimers with RISBZ2/BZP33 and RISBZ3/BZP20 (PubMed:11133985). Interacts with DOF3/RPBF (PubMed:19473328). Specifically expressed in seeds. Expressed in aleurone and subaleurone layers of maturing seeds, but not in the embryo tissues. Expressed in developing seeds from 5 to 20 days after flowering (DAF).