Electron Microscopy Interest Group (EMIG) Seminar: Richard Hite, Ph.D.

Speaker: Richard Hite, Ph.D. (Memorial Sloan Kettering Cancer Center)

Talk Title: Cryo-EM structures of G4-stalled CMG reveal inchworm mechanism of DNA translocation

Abstract: DNA G-quadruplexes (G4s) are non-B-form DNA secondary structures that threaten genome stability by impeding DNA replication. To elucidate how G4s induce replication fork arrest, we have characterized fork collisions with preformed G4s in the parental DNA using reconstituted yeast and human replisomes. We demonstrate that a single G4 in the leading strand template is sufficient to stall replisomes by arresting the CMG helicase. Electron cryomicroscopy structures of stalled yeast and human CMG complexes reveal that the folded G4 is lodged inside the central CMG channel, arresting translocation. The G4 stabilizes the CMG at distinct translocation intermediates, suggesting an unprecedented helical inchworm mechanism for DNA translocation. These findings illuminate the eukaryotic replication fork mechanism under normal and perturbed conditions.