Radiation-Eating Superbug Reveals Gene Secrets

["Sandy Perle" <sandyfl@earthlink.net>]

Friday November 19 1:10 AM ET 

Radiation-Eating Superbug Reveals Gene Secrets  

WASHINGTON (Reuters) - A pink bacterium that shrugs off the worst 
radiation and which has been taught to thrive on toxic waste is 
yielding genetic secrets that could lead not only to better waste 
clean-up but better treatments for cancer, researchers said Thursday. 
 
Teams at The Institute for Genomic Research (TIGR) in Rockville, 
Maryland and at the Department of Energy said they had sequenced the 
genome -- the entire collection of genes -- of Deinococcus 
radiodurans.  

They say it seems to have thousands of unique genes that help it 
clean up the damage done to its DNA by radiation, helping it survive 
where any other creature would die.  

Found living happily 40 years ago in a can of food that had been 
irradiated to kill germs, D. radiourans has intrigued scientists ever 
since.  

It can survive 1.5 million rads of gamma irradiation -- a dose 3,000 
times the amount that would kill a human. It also pops back to life 
after being dried out and can live through high doses of ultraviolet 
radiation.  

Just last year, researchers genetically engineered it to eat up toxic 
chemicals such as toluene and mercury.  

``This is a significant accomplishment,'' Secretary of Energy Bill 
Richardson said in a statement.  

``Besides the insights into the way cells work, this new research may 
help provide a new safe and inexpensive tool for some of the nation's 
most difficult cleanup challenges.''  

The team at TIGR, which has now sequenced the genomes of 10 important 
micro-organisms, used the ``shotgun'' method to make multiple copies 
of every piece of genetic material in the bacterium. Writing in the 
journal Science, they said they overlapped these to make a full map 
of its genes.  

They found about 3,100 genes arranged on two circular chromosomes, 
TIGR president Claire Fraser said.  

The secret to Deinococcus's toughness seems to be a large number of 
genes that allow it not to prevent damage from radiation, heat and 
other assaults, but to repair that damage quickly and efficiently 
enough to allow it to survive.  

Radiation, heat and chemicals create breaks in the double helix of 
DNA that makes up the genes. This can kill a cell outright, or cause 
it to make mistakes as it replicates itself -- mistakes that can kill 
it, or cause cancer and other disease.  

``A unique mechanism may contribute to D. radiourans' resistance to 
DNA damage,'' the researchers wrote in their Science report. ``This 
organism transports damaged nucleotides out of the cell, which 
potentially prevents their reincorporation into the genome.''  

In other words, it throws out the damaged pieces of genetic material. 
 
``Other cells try to recycle building blocks of DNA,'' Fraser said in 
a telephone interview. ``The last thing you want floating around in 
cytoplasm of the cell is a large number of nucleotides that have been 
damaged in some way by the radiation.''  

In addition, the bacterium has other unique genes that must help it 
clean up damage before it causes harm. ``This absolutely has 
implications for understanding DNA damage in cancer,'' Fraser said.  

Many cancers are known to be caused by mutations in the genes 
responsible for fixing damaged DNA.  

``Somewhere between 500 and 1,000 genes in this organism are going to 
be unique to Deinococcus,'' Fraser said. ``My guess is that some are 
absolutely critical to the ability of Deinococcus to withstand 
radiation.''  

A year ago Michael Daly and colleagues at the University of Minnesota 
inserted four genes into Deinococcus that gave it the ability to 
break down some kinds of toxic chemicals and to convert mercury into 
a less dangerous form.  

The Energy Department hopes to make use of genetic information about 
Deinococcus to figure out even better ways to do this. 

-----------------------------------------------------------------------------
Sandy Perle					Tel:(714) 545-0100 / (800) 548-5100   				    	
Director, Technical				Extension 2306 				     	
ICN Worldwide Dosimetry Division		Fax:(714) 668-3149 	                   		    
ICN Biomedicals, Inc.				E-Mail: sandyfl@earthlink.net 				                           
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Costa Mesa, CA 92626

Personal Website:  http://www.geocities.com/scperle
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