The transcriptional activator Opaque2 recognizes two different target sequences in the 22-kD-like α-prolamin genes

Abstract

The maize Opaque2 (O2) protein is a "leucine zipper" DNA binding factor that interacts with the sequence TCCACGTAGA in the promoters of the 22-kD α-zein genes and activates its transcription. A completely different consensus sequence (GATGAPyPuTGPu) identified in b-32, a gene that encodes an abundant albumin that is also under control of the O2 locus, can also be bound by the O2 protein. We showed that the gene encoding the 22-kD-like α-coixin, the α-prolamin of the maize-related grass Coix, can also the transactivited by the O2 protein. A binding assay in vitro and footprint analysis demonstrated that the GACATGTC sequence of the α-coixin promoter can be recognized and protected by the maize O2 protein. Employing transient expression experiments in immature maize endosperm and tobacco mesophyll protoplasts, we demonstrated that the O2 protein can activate expression of the β-glucuronidase reporter gene placed under the control of the 22-kD-like α-coixin promoter. We also demonstrated that a 22-kD-like α-coixin pseudogene promoter is transactivated by the maize O2 protein.