Wednesday, September 22, 2004

Cells of Halobacterium as seen through a high-powered microscope. The individual cells in this image are about 5 microns long.Secrets of a Salty Survivor: "Halobacterium appears to be a master of the complex art of DNA repair. This mastery is what scientists want to learn from: In recent years, a series of experiments by NASA-funded researchers at the University of Maryland has probed the limits of Halobacterium's powers of self-repair, using cutting-edge genetic techniques to see exactly what molecular tricks the 'master' uses to keep its DNA intact.

"'We have completely fragmented their DNA. I mean we have completely destroyed it by bombarding it with [radiation]. And they can reassemble their entire chromosome and put it back into working order within several hours,' says Adrienne Kish, member of the research group studying Halobacterium at the University of Maryland."

A repair enzyme correcting an error in a DNA molecule. The enzyme is on the right in orange and green, and part of the double-helix-shaped DNA is on the left in blue. Image credit: Albert Lau."Halobacterium always keeps a certain amount of repair enzymes on hand, so when a radiation dose occurs, this stash of enzymes can quickly administer 'first aid' to the DNA. But then it must also ramp up production of other repair enzymes to continue the repair, activating the genes that produce those enzymes."

"Halobacterium is something of a 'Renaissance bug.' It dabbles in a bit of everything. Its genome of only 2,400 genes contains several distinct sets of DNA-repair mechanisms. Some of these sets of tools are like the DNA-repair tools found in plants and animals, other sets are more like those of bacteria, and still others are characteristic of a lesser-known group of life called 'Archaea' (the group that Halobacterium belongs to). Halobacterium has them all. Beyond even that, Halobacterium has a few novel DNA-repair mechanisms that no one has ever seen before!

A DNA microarray, as seen through a microscope. Each tiny dot corresponds to one of the organism's thousands of genes, and the color of the dot indicates the activity level of that gene. Image credit: James Smiley."Learning how all these repair mechanisms work could teach scientists a lot about how DNA repair occurs in humans, and perhaps point to ways to enhance people's natural ability to cope with damage to their DNA—a possible boon to astronauts."

"Some of these novel molecular tools could also prove to be useful for industry and biotechnology, DiRuggiero suspects. After all, it was in studying a cousin of Halobacterium—a heat-loving microbe—that scientists found the DNA-copying protein that made it possible to sequence entire genomes. The Human Genome Project would have never happened without it."

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