Every time our cells divide, the DNA inside must be copied accurately to avoid mistakes that could be harmful to our health. Known as DNA synthesis, the precise sequence of steps has until now only been hypothesized. In a recent study, timestamps have been added to step-by-step snapshots, revealing a switch-up between two of the steps that, if replicated in additional studies, would upend our current assumptions of the process.
A team of UC Irvine researchers prepared more than 700 protein samples, each plunged into liquid nitrogen and frozen at a different stage in the DNA synthesis process. The “time-stamped” samples were then analyzed using protein crystallography at the Berkeley Center for Structural Biology‘s beamlines at the Advanced Light Source (ALS).
The data that resulted allowed researchers to arrange the snapshots in the order of their appearance in the reaction pathway, providing the first unambiguous picture of the process—which refuted previous beliefs about the DNA synthesis process. For example, the protein responsible for reading each letter in a DNA strand and building it’s copy, DNA polymerase, showed a reversed process in between two known steps. In this experiment, the protein moved onto reading the next genetic letter before the previous letter’s bonding to the new strand occurred.
This subtle difference in steps could have major implications for developing new approaches to DNA sequencing and therapeutics that halt DNA synthesis in diseased cells, said Nicholas Chim, a researcher in the UC Irvine group and the study’s first author.
This effort was supported in part by the ALS-ENABLE program.
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