Researchers at the University of California, Davis (UC Davis) have visually recorded a key phase in the repair process of damaged human DNA.
Writing about their work in the journal Proceedings of the National Academy of Sciences, the scientists say that the recordings provide new information about the role played by a protein linked to breast cancer, known as Rad51, in this complex and critical process.
Harmful agents like ultraviolet sunlight, tobacco smoke and a myriad of chemicals keep affecting human DNA. Since damage to it can lead to cancer, cell death and mutations, an army of proteins and enzymes are mobilized into action whenever it occurs. The researchers say that Rad51 takes a leading role in the action.
They say that always on call in the cell, molecules of the protein assemble into a long filament along a damaged or broken segment of DNA, where they help stretch out the coiled strands and align them with corresponding segments on the cell's second copy of the chromosome, which serves as a template for reconstruction.
Given the regulation of this protein by a gene linked to increased risk of breast cancer, called BRCA2, it is also thought to play a role in suppression of that disease.
With the ability to watch the assembly of individual filaments of Rad51 in real time, Kowalczykowski's team made a number of discoveries.
They found that Rad51 filaments do not grow indefinitely, which indicates that there is an as-yet undiscovered mechanism that regulates the protein's growth.
They also observed that Rad51 does not fall away from the DNA when repair is complete. Instead, proteins that motor along DNA are required to dislodge it, they say.
"From a practical point of view, being able to record these single molecules gives us insightful information regarding the assembly process. Now we're able to measure this in a quantifiably meaningful way," Kowalczykowski said.