STRUCTURE AND REGULATION OF THE MAIZE BRONZE2 PROMOTER

The maize Bronze2 (Bz2) gene encodes a glutathione S-transferase that is required for anthocyanin pigment accumulation. Two classes of regul atory proteins, R and C1, are required for transcriptional activation of Bz2 and several additional structural genes. Functional domains of the Bz2 promoter were identified using Bz2 promoter-driven luciferase reporter genes electroporated into maize protoplasts together with R a nd C1 expression plasmids. Complete regulation was conferred by 224 nt of the Bz2 promoter. Within this region at least two separable region s are independently capable of conferring regulation by R and C1. Pred icted regulatory elements corresponding to two classes of sequence mot ifs, the Myb-box homologous 'C1-motif', TAACTG/CAGTTA, and the G-box a nd E-box homologous 'R-motif', CACGTG, were shown to be important for full R and C1 activation of the Bz2 promoter. Expression of reconstruc ted Bz2 genes with mutated promoters was quantified using RNase protec tion, and this analysis confirmed results obtained using reporter gene s.