10         20         30         40         50         60
         |          |          |          |          |          |
MEHVISMEEI LGPFWDLPPS PPPLPLPEQQ PLVTDTGSVV IDGVVTQGGG DGEGGDMMGQ - 60
NTTEWTFERL LEEEILINKT TLVTNSSCST LNIDPVVEVD QGTMASGAVS AVGDPMEYNA - 120
ILKRKLEVDL VAFKMWRASS VVNSERSQDS NNHNGGSKNV VQNKLNGEDP INNHAQNVDL - 180
RVRLATSSSS RDPSPSDEDM DGEVEILGFK MPTEERVRKR KESNRESARR SRYRKAAHLK - 240
ELEDQVEQLK AENSCLLRRL AALNQKYNEA NVDNRVLRAD METLRAKVKM GEDSLKRVME - 300
MSSLPPSMPI PALPSSSDAS VPIQDDIINY FSTTPAADED APVDNNSFII MPMADPLQLV - 360
QAEDQPTMGA MELIQKTMGA MPTSPGSALQ ESQLLGLGPD ETINMDMY

Opaque-2 (O2) is a plant bZIP transcription factor that regulates the expression of storage proteins, called prolamines, in the endosperm of maize and Coix seeds. Homozygotic deletion of the O2 gene leads to a phenotypic change in maize seeds from hard glassy kernels to opaque seeds and a decrease in the content of alpha and beta zeins in the endosperm. O2 also seems to be involved in the regulation of lysine catabolism and synthesis of growth precursors in seed. Similar to other plant bZIP transcription factors, O2 can form heterodimers with other bZIP proteins and recognizes many sequences containing the ACGT box, therefore displaying a broad binding specificity and recognizing a variety of target sites in several distinct genes. O2 displays similarity with other bZIPs such as GCN4, c-Fos, and c-Jun.