Structure of Saccharomyces cerevisiae Mediator-RNA polymerase II pre-initiation complex for divergent transcription

The vast majority of eukaryotic promoter regions are divergently transcribed. While divergent transcription serves a key role in shaping the transcriptome, a structural basis for this process remains unexplored. Whether two transcription pre-initiation complexes (PICs) can co-assemble at divergent promotes, and if so, what structural relationships may emerge therefrom, remains unknown. To investigate the structural bases of this phenomenon, we pursued the assembly of the Saccharomyces cerevisiae Mediator-PIC on a divergent promoter. Taking together observations from Cryo-EM, crosslinking-mass spectrometry, and in vitro transcription assays, we were able to capture two distinct PICs co-assembled at divergent promoters, consistent with recent emerging model derived from in vivo observations. Overall, the structure of the Mediator-PIC in this novel form is conducive to transcriptional activation for divergent transcription. © FASEB.