June 27, 2013
‘Junk DNA’ May Not Be So Worthless After All
Rebekah Eliason for redOrbit.com - Your Universe Online
At the center of most human cells, genomic DNA lies tucked away within a nucleus. However, a surprisingly small percentage of this DNA actually codes for genes that can be translated into proteins. In fact, some researchers estimate as much as 98 percent of this DNA seems to have a puzzling lack of purpose, leading many to refer to it as 'junk DNA.' However, a new study from UC San Francisco now emphasizes the potentially important role of DNA residing outside of genes.
Researchers discovered that about 85 percent of the previously labeled junk DNA is vital for making RNA, a versatile molecule with many vital roles within the cell. It was also found that inherited disease risk is more likely associated with RNA-making DNA than other non-gene types of DNA.
As one of the broadest studies of the human genome ever performed to identify RNA-making DNA outside of genes, thousands of previously unidentified RNA sequences were discovered.
Michael McManus, associate professor of microbiology and immunology at the University of California San Francisco and a member of the UCSF Diabetes Center explained these findings saying, "Now that we realize that all these RNA molecules exist and have identified them, the struggle is to understand which are going to have a function that is important. It may take decades to determine this."
Messenger RNA, or mRNA, is the most commonly discussed type and is transcribed from genomic DNA. It is one of the key factors in building proteins from amino acids. Previously, the rest of the DNA was not thought to transcribe RNA, but this new study is changing that idea.
It is still being debated whether RNA molecules transcribed from DNA outside of gene regions play a significant biological role or not. Scientists estimate only 1.5 percent of the human genome is made of DNA that codes for actual genes, but during the last twenty years RNA transcribed from what was thought to be junk DNA has been identified numerous times.
Researchers have discovered thousands of new lincRNA sequences, but only a few are known to be significant to human biology. Previously lincRNA has been shown to have various roles including control of the activity of genes encoding for proteins.
"RNA is the Swiss army knife of molecules . . . it can have so many different functions," McManus explained.
The UCSF researchers took a new look at RNA data from over 125 data sets from 24 types of human body tissue. McManus noted the findings are in general agreement with those reported in September 2012 by researchers associated with a project called ENCODE, which included among its goals the detection of RNA transcripts within the genome.
This study was published in the online journal PLOS Genetics on June 20, 2013.