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DNA Repair Captured in Real Time

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Piero Bianco, PhD

Knowing how DNA unwinds, copies and repairs itself—what starts it, what stops it and why—is vitally important to recombinant DNA research and will make possible major advancements in cancer treatment.

Piero Bianco, PhD, is the first person to film a DNA motor protein “unzipping” a double-strand of bacterial DNA.

Knowing how DNA unwinds, copies and repairs itself—what starts it, what stops it and why—is vitally important to recombinant DNA research and could make possible major advancements in cancer treatment.

DNA motor proteins are natural drug targets because they allow DNA to copy and repair itself, causing the uncontrolled cell growth in cancer. Researchers know that many cancer drugs stop cell growth, but they don’t know precisely how.

Developed Laser Tweezer Technique to Observe Repair

Bianco, an associate professor of microbiology and immunology, is providing important clues.

To make his movies, he uses a technique he developed called “laser tweezers,” which he combines with fluorescence microscopy and laminar flow cells to isolate individual molecules of DNA and observe the action of the repair machinery in real time.

Bianco developed his system while a postdoctoral fellow at the University of California at Davis, in collaboration with researchers from Lawrence Livermore National Laboratory.

The work culminated in a breakthrough film, which Bianco and colleagues described in the journal Nature (“Processive translocation and DNA unwinding by individual RecBCD enzyme molecules”).

The film features a molecule of Escherichia coli helicase, called RecBCD, which acts by unzipping the DNA molecule from one end to the other.

Since then, Bianco has made significant improvements to his filming technique that have resulted in higher-resolution movies.

Films Depict Two Proteins Driving Recombination

Bianco also has adapted his system to investigate other, more complex bacterial helicases, including RuvAB, a motor protein that drives a critical late step in genetic recombination called branch migration.

He is making a series of films that depict, for the first time, how two key proteins work together in humans to drive recombination and the exchange of genetic information.

The first, Rad54, is a motor protein. The second, Rad51, is a type of enzyme known as a recombinase, which catalyzes the exchange of strands of DNA between two DNA molecules, particularly in paired maternal and paternal chromosomes.

Bianco has shown that when DNA is collapsed around the recombinase, it makes it exponentially faster for Rad51 to locate the correct spot on a strand needing repair.

Working to Assemble Full Recombination Reaction

Bianco’s work goes to the heart of one of the biggest mysteries in recombinant DNA research: What biomechanical processes are involved in invading a damaged strand of DNA and how to find the repair target—a question that has enormous implications for drug development.

He is now working toward his long-term goal: assembling an entire recombination reaction.