Re: News: New Nucleotide In DNA Could Revolutionize Epigenetics

In article <gsae44$22f8$1@xxxxxxxxxxxxxxxxxxx>, "Robert Karl Stonjek" <rstonjek@xxxxxxxxxxxxxx> wrote:
New Nucleotide In DNA Could Revolutionize Epigenetics
ScienceDaily (Apr. 17, 2009) - Anyone who studied a little genetics in high
school has heard of adenine, thymine, guanine and cytosine - the A, T, G and
C that make up the DNA code. But those are not the whole story. The rise of
epigenetics in the past decade has drawn attention to a fifth nucleotide,
5-methylcytosine (5-mC), that sometimes replaces cytosine in the famous DNA
double helix to regulate which genes are expressed. And now there's a sixth:
5-hydroxymethylcytosine.

"Now"? 5-hydroxymethylcytosine has been known foir ages. E.g.,
and abstract from Biochem J. 1972 February; 126(4): 781?790 says:
"[rat brain DNA] contains 5-hydroxymethylcytosine at a content of
about 15% of the total cytosine bases present".

The discovery of a new nucleotide may make biologists rethink their
approaches to investigating DNA methylation.

"The discovery"? LOL. Scientific journalism at its best. This discovery
is at least 45 years old.

Ironically, the latest addition
to the DNA vocabulary was found by chance during investigations of the level
of 5-methylcytosine in the very large nuclei of Purkinje cells, says
Skirmantas Kriaucionis, a postdoctoral associate in the Heintz lab, who did
the research. "We didn't go looking for this modification," he says. "We
just found it."

Kriaucionis was working to compare the levels of 5-methylcytosine in two
very different but connected neurons in the mouse brain - Purkinje cells,
the largest brain cells, and granule cells, the most numerous and among the
smallest. Together, these two types of cells coordinate motor function in
the cerebellum. After developing a new method to separate the nuclei of
individual cell types from one another, Kriaucionis was analyzing the
epigenetic makeup of the cells when he came across substantial amounts of an
unexpected and anomalous nucleotide, which he labeled 'x.'

"Unexpected"? This only means the researches were completely ignorant
of the textbook-level material in their own field.

It accounted for roughly 40 percent of the methylated cytosine in Purkinje
cells and 10 percent in granule neurons. He then performed a series of tests
on 'x,' including mass spectrometry, which determines the elemental
components of molecules by breaking them down into their constituent parts,
charging the particles and measuring their mass-to-charge ratio. He repeated
the experiments more than 10 times and came up with the same result: x was
5-hydroxymethylcytosine, a stable nucleotide previously observed only in the
simplest of life forms, bacterial viruses.

Shows how well we teach our Ph.D. students and HHMI investigators...

DK

.

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