New Nucleotides Identified in Human DNA

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When scientists talk of DNA sequencing, it's written as strings of these letters: A, T, C, G.
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THE GIST

- Researchers added and removed methyl groups to identify these new nucleotides.

- The list of DNA nucleotides had been previously increased from four to six.

- The discovery could someday advance the field of stem cell research.

The human recipe just got complicated: It turns out there are more ingredients in us than we thought.

In high school science, we were taught of the four basic units that make up DNA -- adenine, guanine, thymine and cytosine. When scientists talk of DNA sequencing, it's written as strings of these units: ATCGGTGA, and so on.

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In recent years, scientists expanded that list of nucleotides from four to six. And in a study published online in the most recent issue of Science magazine, researchers from the University of North Carolina School's medical school have discovered the seventh and eight bases of DNA.

But the meaning of this extra ingredient in the alphabet soup that makes us who we are isn't as simple as A, B, C.

"Before we can grasp the magnitude of this discovery, we have to figure out the function of these new bases," said Yi Zhang, biochemistry and biophysics professor at UNC's Howard Hughes Medical Institute.

Zhang arrived at his discovery by playing around with the chemical makeup of the base cytosine; by adding a new chemical tag -- called a methyl group -- to the base it became those fifth and sixth units. This process, called methylation,causes the DNA's double helix to fold even tighter upon itself.

Demethylation describes the removal of a chemical group from a molecule, a process that led to the new 7th and 8th units -- they've been given the ugly names 5-formylcytosine and 5 carboxylcytosine. (The fifth base -- 5 methylC -- and the sixth base -- 5 hydroxymethylC -- have equally ungainly names, to be fair.)

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"These bases represent an intermediate state in the demethylation process," he explained.

Once better understood, Zhang hopes his discovery could someday advance the field of stem cell research. By demethylating DNA, it may be possible to reprogram adult cells to make them act like stem cells.

It could also inform cancer research, as it could give scientists the opportunity to reactivate tumor suppressor genes that had been silenced.

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