Structural basis of a transcription pre-initiation complex on a divergent promoter

• DOI: 10.1016/j.molcel.2023.01.011
• Publication Date: 2023-02-01T16:24:23Z
• Authors: Jose J. Gorbea Colón; Leon Palao; Shin-Fu Chen; Hee Jong Kim; Laura Snyder; Yi-Wei Chang; Kuang-Lei Tsai; Kenji Murakami
• Keywords: 0301 basic medicine; 03 medical and health sciences; Saccharomyces cerevisiae Proteins; Mediator Complex; Transcription, Genetic; Cryoelectron Microscopy; RNA Polymerase II; Saccharomyces cerevisiae; Promoter Regions, Genetic; Transcription Initiation, Genetic

Most eukaryotic promoter regions are divergently transcribed. As the RNA polymerase II pre-initiation complex (PIC) is intrinsically asymmetric and responsible for transcription in a single direction, it is unknown how divergent transcription arises. Here, the Saccharomyces cerevisiae Mediator complexed with a PIC (Med-PIC) was assembled on a divergent promoter and analyzed by cryoelectron microscopy. The structure reveals two distinct Med-PICs forming a dimer through the Mediator tail module, induced by a homodimeric activator protein localized near the dimerization interface. The tail dimer is associated with ∼80-bp upstream DNA, such that two flanking core promoter regions are positioned and oriented in a suitable form for PIC assembly in opposite directions. Also, cryoelectron tomography visualized the progress of the PIC assembly on the two core promoter regions, providing direct evidence for the role of the Med-PIC dimer in divergent transcription.