Regulatory Specificity of the Maize Myb-Domain Proteins P and C1

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9723355 Grotewold Transcription factors frequently belong to families of proteins that share related DNA-binding domains and bind similar DNA sequences. Yet, these factors are able to regulate different cellular processes by activating specific sets of target genes. It is therefore fundamentally important to understand the mechanisms by which transcriptional regulators with similar DNA-binding domains direct specific patterns of gene expression to achieve biological specificity. This research will investigate the mechanisms by which P and C1, two maize proteins related to the Myb oncogene, regulate the accumulation of different flavonoid pigments by activating overlapping sets of biosynthetic genes. Our previous studies showed that P and C1 encode sequence-specific DNA-binding proteins that recognize with different affinities identical cis-acting promoter elements in a commonly regulated gene. Whereas C1 requires the bHLH factors of the R/B family for regulatory function, P does not, but may require other as yet-unidentified cellular factors to regulate promoters lacking high-affinity P-binding sites. How combinatorial interactions with accessory factors modulate P and C1 regulatory function is not known. Previous studies have also shown that the conserved Myb-domains of these proteins are sufficient for their regulatory specificity: The Myb domain is solely responsible for the DNA-binding properties of these proteins, and the Myb-domain of C1 mediates the interaction with the R/B proteins, indicating a need to elucidate the structure of Myb-domains to understand how biological specificity is achieved. To determine how P and C1 regulate specific patterns of gene expression and to understand how plant Myb-domain proteins achieve biological specificity, we will determine the residues in C1 that allow it, but not P, to interact with R/B. Since the interaction of C1 with R/B proteins is fundamental for C1 function, we will investigate why C1 requires R/B, whereas P does not. We will inv estigate whether additional cellular factors are required for the regulatory function of P and C1. This question is important because neither P nor C1+R/B are sufficient to regulate promoters lacking high-affinity DNA-binding sites for these proteins. This research will contribute to a fundamental understanding of the mechanisms used by transcription factors to regulate the expression of different genes to achieve biological specificity. %%% Regulation of gene expression is a central process in all living organisms. Transcription factors frequently belong to families of proteins that share related DNA-binding domains and bind similar DNA sequences. Yet, these factors are able to regulate different cellular processes by activating specific sets of target genes. It is therefore important to understand how transcriptional regulators with similar DNA-binding domains achieve biological specificity in directing specific patterns of gene expression. Our approach to this biological question is to investigate the mechanisms by which two maize proteins related to the Myb oncogene regulate the accumulation of different flavonoid pigments by activating overlapping sets of biosynthetic genes. This research will contribute to a fundamental understanding of the mechanisms used by transcription factors, to regulate the expression of different genes to achieve biological specificity. ***