Stressed cells spark DNA repair missteps and speed evolution
When Dr. Susan Rosenberg, professor of molecular and human genetics at Baylor College of Medicine, first published her finding that the mutation rate increased in bacteria stressed by starvation, sometimes resulting in a rare change that benefited the bacteria, it was controversial.
In a report in the current issue of the journal Molecular Cell, she and her colleagues describe not only how it happens but also show that this only occurs at a special time and place in the stressed cells.
It all begins with the way that the cell repairs breaks in the double strands of DNA that are its genetic blue print. Usually, when this happens, special protein machinery in the cell copies the missing DNA from another chromosome and rejoins the broken ends around the newly synthesized genetic material.
"It fixes the hole in the DNA by copying similar information," said Rosenberg. However, when the process goes wrong, the repair process introduces errors into the DNA.
When graduate student Rebecca G. Ponder set up a system so that she could control where the break in DNA occurred, she found that errors occurred right next to the break in the stressed cells, and that the rate of errors was 6,000 fold higher than in cells whose DNA was not broken. "Its really about local repair," said Rosenberg. Not only that, but subsequent experiments proved that this mechanism of increased mutation at sites of DNA repair occurs only in the cells under stress. "Even if you get a break in a cell, it wont process it in a mutagenic way," said Rosenberg. "The cell repairs it, but does not make mutations unless the cell is stressed."
The findings support the notion that the increased mutation rate may give the cells a selective advantage, she said. Faced with starvation, most cells do not increase their mutation rate. Then if food becomes available again, they do well.
Among the small percentage that do increase mutations, most of the errors are neutral, not affecting cells at all. Many are deleterious, resulting in cell death. But a small percentage is advantageous, allowing the cells to survive in an adverse environment.
The fact that the changes in the rate of mutation occur only in a certain physical space at a certain time gives the cells advantage because it reduces the risk to the whole colony. DNA breaks occur only rarely in each individual cell. If the mutations are restricted in time and space, it reduces the risk that the mistakes in repair will affect some other gene. It can also enhance the likelihood of two mutations occurring in the same gene or neighboring genes.
"This can speed evolution of complex protein machines." Rosenberg said.
Ross Tomlin | EurekAlert!
The most recent press releases about innovation >>>
Die letzten 5 Focus-News des innovations-reports im Überblick:
X-ray study throws light on key process for production
A Swedish-German team of researchers has cleared up a key process for the artificial production of silk. With the help of the intense X-rays from DESY's...
For the first time ever, a cloud of ultra-cold atoms has been successfully created in space on board of a sounding rocket. The MAIUS mission demonstrates that quantum optical sensors can be operated even in harsh environments like space – a prerequi-site for finding answers to the most challenging questions of fundamental physics and an important innovation driver for everyday applications.
According to Albert Einstein's Equivalence Principle, all bodies are accelerated at the same rate by the Earth's gravity, regardless of their properties. This...
New success for Konstanz physicists in studying the quantum vacuum
An important step towards a completely new experimental access to quantum physics has been made at University of Konstanz. The team of scientists headed by...
HZI researchers decipher infection mechanisms of Yersinia and immune responses of the host
Yersiniae cause severe intestinal infections. Studies using Yersinia pseudotuberculosis as a model organism aim to elucidate the infection mechanisms of these...
Researchers from the University of Hamburg in Germany, in collaboration with colleagues from the University of Aarhus in Denmark, have synthesized a new superconducting material by growing a few layers of an antiferromagnetic transition-metal chalcogenide on a bismuth-based topological insulator, both being non-superconducting materials.
While superconductivity and magnetism are generally believed to be mutually exclusive, surprisingly, in this new material, superconducting correlations...