DNA repair: it's better to see it once...
Scientists followed the DNA scanning with repair proteinsNanoNewsNet based on ScienceDaily: Quantum Dots Spotlight DNA-Repair Proteins in Motion
Repair proteins effectively scan our genome, find errors, jumping like fleas between DNA molecules, sliding along their chains and, possibly, making stops in suspicious places.
This is the opinion of scientists from the University of Pittsburgh (University of Pittsburgh), the University of Essex (University of Essex) and the University of Vermont (University of Vermont), who marked proteins with quantum dots to consider the unfolding actions.
We are all constantly bombarded by environmental toxins that cause "errors" in our DNA. Therefore, the rapid repair system is very important for maintaining the integrity of DNA sequences and adequate cell function, explains Bennett Van Houten, PhD, professor of the Department of Molecular Oncology and head of the Molecular and Cellular Biology of Cancer Program at the University of Pittsburgh Cancer Institute, Professor of the Department of Pharmacology and Chemical Biology University of Pittsburgh School of Medicine.
How this system works is an important question that has no answer yet," he says. – It should be able to identify very small errors in the three-dimensional organization of gene chains. It's like finding potholes on every street across the country and having time to repair them before the next rush hour.
Scientists tried to solve the mystery by marking two repair proteins, uvrA and UvrB, with quantum dots – semiconductor nanocrystals glowing in different colors. To see the process more clearly, they also stretched the usually spiralized DNA molecule into several straight strands.
The researchers observed how the uvrA protein randomly jumps from one DNA molecule to another, lingering in one place for seven seconds. But when the uvrA protein formed a complex with two UvrB (UvrAB) protein molecules, a new, more efficient mechanism began to operate: the complex slid along the DNA strand for 40 seconds. Then it also separated from one DNA molecule and jumped to another.
If the E.coli bacterium has only one UvrAB complex, 13 hours will be enough for the entire genome to be scanned, says lead researcher Neil M. Kad (Department of Biological Sciences, University of Essex, UK). – About 40 complexes, which is comparable to what scientists already know, will be required to scan its genome in 20 minutes – the time of division of the bacterium.
In addition to random jumps and sliding, the scientists also observed what they called "suspended motion," in which the movement of the UvrAB complex seemed slower and more purposeful.
About one–third of the mobile molecules we studied behave this way," says co-author David M. Warshaw, professor and dean of the Faculty of Molecular Physiology and Biophysics at the University of Vermont. – Suspension of movement may be a check by UvrAB complexes of structural anomalies associated with DNA damage.
Now scientists are studying the possibility that complexes analyze the shape or chemical configuration of a DNA molecule by interacting with it. The error can change the local structure of DNA, changing its compatibility with repair proteins and possibly causing a corrective response.
The results of the study are published in Molecular Cell (Neil M. Kad et al., Collaborative Dynamic DNA Scanning by Nucleotide Excision Repair Proteins Investigated by Single-Molecule Imaging of Quantum-Dot-Labeled Proteins).
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