MEXICO: The first-ever images of the protein complex that unwinds, splits, and copies double-stranded DNA reveal something rather different from the standard textbook view. The electron microscope images, created by scientists at the U.S. Department of Energy’s Brookhaven National Laboratory with partners from Stony Brook University and Rockefeller University, offer new insight into how this molecular machinery functions, including new possibilities about its role in DNA “quality control” and cell differentiation. The images and implications are described in a paper published online by the journal Nature Structural & Molecular Biology, November 2, 2015.
“This work is a continuation of our long-standing research using electron microscopy to understand the mechanism of DNA replication, an essential function for every living cell,” said Huilin Li, a biologist with a joint appointment at Brookhaven Lab and Stony Brook University. “These new images show the fully assembled and fully activated ‘helicase’ protein complex-which encircles and separates the two strands of the DNA double helix as it passes through a central pore in the structure-and how the helicase coordinates with the two ‘polymerase’ enzymes that duplicate each strand to copy the genome.”
Studying this molecular machinery, known collectively as a “replisome,” and the details of its DNA-copying process can help scientists understand what happens when DNA is miscopied-a major source of mutation that can lead to cancer-or learn more about how a single cell can eventually develop into the many cell types that make up a multicellular organism. But no one has produced a real structure of a replisome at any resolution for any organism until now.
