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Time to retrieve junk DNA from the trashcan

Sun, 25th Jan 2009

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Scientists have discovered a role for the DNA that makes up the majority of the genome but which had previously been written off as rubbish.

DNA fragmentWriting in the journal Molecular Cell, Edinburgh University researcher David Tollervey and his colleagues explain how these non-coding segments of DNA, which lie between the known genes, actually give rise to a large number of chemical messengers that regulate the control of other genes.  Working with yeast cells, which are very similar albeit slightly simpler than human cells, the researchers found that the non-coding DNA produces sequences of its chemical relative RNA.

Normally, RNA molecules are used to translate the genetic recipes written into the genome into proteins that carry out important functions in a cell.  But these so-called non-coding RNAs that the Edinburgh team have been studying are different. 

Instead they are used to control the addition or removal of chemical tags (methyl or acetyl groups) from the DNA and this process, known as histone modification, can powerfully affect the activity of the tagged gene.

"Cells contain about 2 metres of DNA, which needs to be tightly packaged within the nucleus," explains Tollervey. "This is achieved by winding the DNA into a tight configuration called chromatin.  But by modifying the DNA through the addition of these chemicals cells are able to ensure that certain genes remain accessible and active."

This is the chemical-equivalent of moving the things you use most often to the front of your cupboards so that they are easier to reach.

"We think that this process allows the yeast to control its gene activity more tightly to take advantage of different environmental conditions or food sources," says Tollervey.  But in humans it also answers another important question - why we can get away with having fewer genes than a banana!

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