Yeast Mediator facilitates transcription initiation at most promoters via a Tail-independent mechanism

Mediator (MED) is a conserved factor with important roles in basal and activated transcription. Here, we investigate the genome-wide roles of yeast MED by rapid depletion of its activator-binding domain (Tail) and monitoring changes in nascent transcription. Rapid Tail depletion surprisingly reduces transcrip-tion from only a small subset of genes. At most of these Tail-dependent genes, in unperturbed conditions, MED is detected at both the UASs and promoters. In contrast, at most Tail-independent genes, we find MED primarily at promoters but not at the UASs. These results suggest that MED Tail and activator -medi-ated MED recruitment regulates only a small subset of genes. Furthermore, we define three classes of genes that differ in PIC assembly pathways and the requirements for MED Tail, SAGA, TFIID, and BET factors Bdf1/ 2. Our combined results have broad implications for the roles of MED, other coactivators, and mechanisms of transcriptional regulation at different gene classes.

Automated summary

This study investigates the genome-wide roles of the mediator factor (MED) in transcription. Rapid depletion of the activator-binding domain (Tail) of MED reveals that it only regulates a small subset of genes. The study also classifies genes into tail-dependent and tail-independent categories and discusses their implications for MED, other coactivators, and transcriptional regulation mechanisms.