Systematic identification of transcriptional activation domains from non-transcription factor proteins in plants and yeast
Transcription factors can promote gene expression through activation domains. Whole-genome screens have systematically mapped activation domains in transcription factors, but not in non-transcription factor proteins (e.g., chromatin regulators, coactivators). To fill this knowledge gap, we employed the activation domain predictor PADDLE to analyze the proteomes of Arabidopsis thaliana and Saccharomyces cerevisiae. We screened 18,000 predicted activation domains from >800 non-transcription factor genes in both species, confirming that 89% of candidate proteins contain active fragments. Our work enables the annotation of hundreds of nuclear proteins as putative coactivators, many of which have never been ascribed any function in plants. Analysis of peptide sequence compositions reveals how the distribution of key amino acids dictates activity. Finally, we validated short, 'universal' activation domains with comparable performance to state-of-the-art activation domains used for genome engineering. Our approach enables the genome-wide discovery and annotation of activation domains that can function across diverse eukaryotes. Overall design: To measure transcriptional activation domain activity, we used FACS to separate cells with different GFP levels of a reporter construct. We sequenced the barcodes attached to each activation domain in each sorted population.