Monday, January 6, 2014

Scientists discover double meaning in genetic code

A team of researchers have made the discovery that the genetic code used by DNA to store information actually contains a double meaning, with the second set of coded information having major implications for how scientists read and interpret the instructions within it.  According to the authors of this study, this fascinating find could help them to better understand both disease and health.
DNA, or deoxyribonucleic acid, is present in the cells of all humans, as well as almost every other living organism.  It contains the information for building and maintaining an organism in the form of a chemical code.  Four basic chemical bases – adenine, guanine, cytosine and thymine – are strung together in various sequences; and, the sequencing of these bases is what determines what information is coded within them, much like letters of the alphabet can be put together to create many different words and sentences.
The overall structure of DNA is what is known as a double helix.  The bases of DNA pair up with each other, with adenine pairing with thymine and cytosine pairing with guanine.  Each base pair then attaches to a sugar molecule as well as a phosphate molecule and this complete package is called a nucleotide.  Sequences of nucleotides arrange themselves in two long strands, somewhat like a ladder joined by base pair rungs, and the DNA molecule takes on a spiraling, helical shape.
DNA is able to make copies of itself by “unzipping” its two strands, allowing each strand to serve as a template for new DNA to be formed.  This process is how new DNA is created whenever cells divide and multiply.
Since 1962, when James Watson and Francis Crick received the Nobel Prize in Physiology or Medicine for discovering DNA, it has been thought that this was all there was to know about how DNA worked.  However, a research team lead by Dr. John Stamatoyannopoulos of the University of Washington, has made a startling new discovery.  DNA is actually used to write in two different languages, giving a double meaning to the genetic code.
One of these languages, the one that was discovered by Watson and Crick, is used to code information about proteins.   The second one, which was just discovered, codes information which tells the cell how to control genes.  Genes are sections of DNA molecules which, when taken by themselves, code for specific proteins.  Humans have thousands of genes, all of them controlling different traits, such as eye color or height.
It took scientists a long time to locate this second language because one language is superimposed over the other one.
Speaking about this new find,  Stamatoyannopoulos note that “[t]hese new findings highlight that DNA is an incredibly powerful information storage device, which nature has fully exploited in unexpected ways.”
According to the UW team, the genetic code uses a 64-letter “alphabet” called codons.  What they discovered in their work was that some of these codons actually had two different meanings, one which affected protein sequencing and one which affected gene control.  These codons, which they call duons, seem to have evolved these double meanings in order to help stabilize certain beneficial features of proteins and their manufacture.
Their findings have important implications for how scientists interpret a person’s genome, they say, opening up new ways to diagnose and treat disease.  Because the genetic code is communicating two different types of information at the same time, diseases which appear to be the result of alterations in protein sequencing might actually be caused by changes in gene control programs, or even both factors.
The findings from the study were published in the December 13, 2013 issue of Science.
By Nancy Schimelpfening