Sumoylation of Rap1 mediates recruitment of the basal transcription machinery to promote transcription of Ribosomal Protein genes

Transcription factors are among the most abundant Sumo targets, yet the global distribution of Sumo along the chromatin and its physiological relevance in transcription are poorly understood. We show that in Saccharomyces cerevisiae Sumo is significantly enriched at 631 genes, mainly with functions in translation and cellular homeostasis. Contrary to common belief, Sumo positively affects transcription at most genes. Sumo levels are highest at RNAPIII-transcribed genes and at ribosomal protein genes (RPGs), and we show that the Sumo consensus motif at RPG promoters is identical to the DNA binding motif of the transcription factor Rap1. We demonstrate that Rap1 is the molecular target of Sumo, that Rap1 sumoylation promotes recruitment of the basal transcription machinery, and that the Sumo-Rap1 and target of rapamycin kinase complex 1 (TORC1) pathways cooperate in RPG transcription. Finally, our data indicate that sumoylation of Rap1 functions in a homeostatic feedback loop that sustains RPG transcription.

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