Homodimeric and heterodimeric leucine zipper proteins and nuclear factors from parsley recognize diverse promoter elements with ACGT cores.

Four short nucleotide sequences (boxes I to IV) contribute to the light responsiveness of the parsley chalcone synthase promoter. The sequence-related boxes II and III resemble several plant, viral, and bacterial promoter elements that share ACGT core sequences and are associated with diversely regulated genes. We have analyzed the binding characteristics and protein-protein interactions of factors from nuclear extracts and of three putative leucine zipper (bZIP) transcription factors potentially involved in the regulation of this promoter. These common plant regulatory factors (CPRFs) bind specifically to boxes II and III as well as other ACGT-containing promoter elements (hex1, Em1a, and as-1), though with markedly different affinities. Intact bZIP domains are crucial for CPRF binding to DNA. Distinct ensembles of nuclear factors bind to boxes II and III, despite their sequence similarity. The parsley CPRFs bind to DNA as dimers, selectively form heterodimeric DNA binding complexes, and interact with nuclear proteins.