Three-dimensional structure of the genome replication machine discovered

"DNA polymerase delta serves as the duplicating machine for the millions to billions of base pairs in human and other genomes. We were able to present for the first time a near-atomic-resolution structure of the complete enzyme in the act of DNA synthesis," says lead investigator Aneel Aggarwal, PhD, Professor of Pharmacological Sciences at the Icahn School of Medicine at Mount Sinai. "This knowledge furthers our basic understanding of this complex enzyme which is essential for survival in higher organisms from humans to yeast. At the same time, our work provides insights into how cancers can arise when DNA polymerase delta is not functioning properly, and offers a novel basis for designing inhibitors of the polymerase that could potentially serve as effective treatment in certain cancers."

While DNA polymerase delta has been studied by scientists for decades, many questions remain about its overall architecture and dynamics. "We showed how the various pieces of this complicated machine work synchronously with one another to copy the genome with amazing accuracy," explains Dr. Aggarwal. His team, which included co-author Rinku Jain, PhD, Assistant Professor of Pharmacological Sciences at the Icahn School of Medicine, also mapped a number of inherited mutations (which are passed down from parent to child) and somatic mutations (which occur by chance during someone's lifetime) in DNA polymerase delta that are associated with "hypermutated" tumors. In addition to cancers, these mutations may be associated with multi-symptom mandibular hypoplasia, deafness, and lipodystrophy syndrome.

Essential to the Mount Sinai researchers' work were recent advances in cryo-electron microscopy. This technology, which allows for the imaging of rapidly frozen molecules in solution, is revolutionizing the field of structural biology through its high-resolution pictures. This technique allowed Dr. Aggarwal and his team to examine not only individual atoms of the DNA polymerase delta but also how they move to achieve accurate replication of the genome. Integral to this phase of the research was Mount Sinai's partnership with the Simons Electron Microscopy Center in New York City.

Building on its latest groundbreaking work around DNA polymerase delta, Mount Sinai will continue to explore the unique structure and mechanism of the polymerase, particularly its relationship to cancer and disease pathogenesis. "We know that certain cancers become dependent on this enzyme for their survival," says Dr. Aggarwal, "and inhibiting its activity could provide a valuable therapeutic window for future medical research."