Todd Matulnik, J. Marcela Hernandez and Erich Grotewold

The Ohio State University, Columbus, OH 43210

In maize, several pigmentation metabolic pathway genes are alternately regulated by a set of transcription factors. The myb domain proteins P and C1 are 69% identical at the amino acid level and recognize the same A1 promoter sequences, however, their modes of operation are very distinct. C1 absolutely requires one of the basic helix-loop-helix motif proteins B or R to activate production of the anthocyanin pathway in the kernel aleurone layer while the independently operating P directs phlobaphene synthesis in pericarp tissues. When the Myb domain of P is fused to the Gal4 activation domain (P^myb:Gal4^AD) it is capable of activating transcription in yeast from a minimal promoter containing A1 binding sequences. The C1^myb:Gal4^AD construct is incapable of activating from the same promoter, even when B is present, indicating that a few amino acid changes between P and C1 Myb domains are sufficient to account for the very different activity of these proteins. Currently, experiments are underway to produce a P-mimic by exchanging specific C1 amino acids to P-like residues and produce an independent functioning C1^myb:Gal4^AD. Similar experiments altering P to cause a P^myb:Gal4^AD which requires B to function, i.e C1-like, are also being pursued. The ultimate goal of each experiment is to expand our knowledge of transcription factors and to direct the evolution of novel transcription factors whose DNA binding as well as protein-protein interactions can be manipulated to improve control of metabolism and transgenes.