Cells can read damaged DNA without missing a beat

Feb 09, 2010

Scientists have shown that cells' DNA-reading machinery can skim through certain kinds of damaged DNA without skipping any letters in the genetic "text." The studies, performed in bacteria, suggest a new mechanism that can allow bacteria to develop resistance to antibiotics.

The results were published online this week in the . The senior author is Paul Doetsch, PhD, professor of biochemistry and at Emory University School of Medicine and associate director for basic research at Winship Cancer Institute of Emory University.

Working with Doetsch, graduate student Cheryl Clauson examined the ability of RNA polymerase (the enzyme that transcribes, or makes RNA from DNA) to handle damaged DNA templates.

RNA polymerase reads one strand of the and assembles RNA that is complementary to that strand. In test tube experiments, when the enzyme comes to a gap or a blank space, it keeps reading but leaves out letters across from the damaged stretch. In contrast, in cells, RNA polymerase puts a random letter (preferring A) across from the gap.

"We were surprised to find that the transcription machinery rolls right over the damaged portion," Doetsch says. "This shows that if the cell initiates, but doesn't complete repair, it still can lead to mutagenesis."

Clauson says a challenge in planning her experiments was finding a way to sensitively detect when RNA polymerase reads through .

She loaded damaged DNA into a gene that encodes an enzyme from fireflies, which generates light-emitting chemicals, and then introduced that gene into bacteria. A full working enzyme is produced only if bypasses the DNA damage without skipping any letters.

DNA in every type of cell, whether bacterial, plant or animal, is constantly being damaged by heat, oxygen and radiation. In addition, all cells make RNA from some of their genes to produce proteins and carry out their normal functions. Cells periodically copy their DNA before dividing, but only if conditions are right for them to grow.

The experiments were performed in bacteria with mutations disabling some forms of DNA repair, Clauson says.

"This situation may resemble one where something like radiation or a mutagenic chemical has overwhelmed the normal repair mechanisms," she says.

In addition, Clauson used an antibiotic called novobiocin to shut down DNA replication in the bacteria. She says this simulates a more challenging environment when cells are not growing quickly.

"Our ability to see transcriptional mutagenesis in growth-limiting conditions is important," Doetsch says. "Out in the environment, bacteria are not constantly surrounded by the rich mix of nutrients we give them in the lab."

"Because this work hints at a simple mechanism by which bacteria could escape from growth-restricted environments, it has important implications for how pathogenic microorganisms may acquire resistance to antibiotics," he adds. The next phase of these studies for Doetsch and colleagues will be to test whether transcriptional mutagenesis can lead directly to antibiotic resistance in and other microorganisms.

Explore further: Bulletproof nuclei? Stem cells exhibit unusual absorption property

More information: C.L. Clauson, K.J. Oestreich, J.W. Austin and P.W. Doetsch. Abasic sites and strand breaks in DNA cause transcriptional mutagenesis in Escherichia coli. PNAS Early Edition (2010)

Related Stories

DNA repair mechanisms relocate in response to stress

Mar 26, 2009

Like doctors making house calls, some DNA repair enzymes can relocate to the part of the cell that needs their help, a collaborative team of scientists at Emory University School of Medicine has found.

Scientists discover role of enzyme in DNA repair

Jun 27, 2007

Scientists from the National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), National Cancer Institute (NCI), and Integrative Bioinformatics Inc. have made an important discovery about the role of an ...

Recommended for you

Researchers successfully clone adult human stem cells

Apr 18, 2014

(Phys.org) —An international team of researchers, led by Robert Lanza, of Advanced Cell Technology, has announced that they have performed the first successful cloning of adult human skin cells into stem ...

Researchers develop new model of cellular movement

Apr 18, 2014

(Phys.org) —Cell movement plays an important role in a host of biological functions from embryonic development to repairing wounded tissue. It also enables cancer cells to break free from their sites of ...

User comments : 0

More news stories

Biologists help solve fungi mysteries

(Phys.org) —A new genetic analysis revealing the previously unknown biodiversity and distribution of thousands of fungi in North America might also reveal a previously underappreciated contributor to climate ...

Poll: Big Bang a big question for most Americans

Few Americans question that smoking causes cancer. But they have more skepticism than confidence in global warming, the age of the Earth and evolution and have the most trouble believing a Big Bang created the universe 13.8 ...

Making graphene in your kitchen

Graphene has been touted as a wonder material—the world's thinnest substance, but super-strong. Now scientists say it is so easy to make you could produce some in your kitchen.