A, T, G, C and What?

I don't understand. We've sequenced mouse genomes thousands of times before, how have we never noticed? Does this nucleotide not exist in the actual genome, but is free-floating in the cell? Or does this nucleotide appear like one of the traditional 4 when we run sequencing tests? Can anyone help me out?

5-hydroxymethylcytosine is the methylated form of cytosine, not a new nucleotide.

So this nucleotide would still code for the same amino acid if it was in the genetic sequence? Why is this so groundbreaking as : the reason why humans and other animals are so different?

Methylation is an epigenetic factor. Epigenetics is the study of factors that influence how our DNA is read and processed, w/o directly affecting the code itself. The methylation of the parent can affect what genes are expressed in offspring. Look up epigenetics on wikipedia for a bigger explanation; which popsci should have done before posting this incredibly wrong article.

5-hydroxymethylcytosine is different from methylated cytosine. While it has been long known to exist in bacteriophage DNA, it was surprising to find in human DNA. It would not be detected by normal sequencing methods. It was noticed when they consistently observed a significantly lower amount of methylated-cytosine in their Purkinje DNA samples and the presence of a unidentified spot on their thin-layer chromatography plates. hdmC was found to comprises 0.6% of total nucleotides in Purkinje cell DNA, 0.2% in granule cells, and is not present in cancer cell lines. It is nearly 40% as abundant as methylated-C in Purkinje cell DNA. I is enriched in the brain, suggesting a role in epigenetic control of neuronal function.

Really misleading and sensationalist article. It's not a new "building block" because the change to the nucleotide (the extra hydroxymethyl group) only occurs in certain genes in certain cells (neurons in this case). It's not something that's part of the DNA that will be passed on to offspring. Epigenetic modifications like this occur in all animals.

Also, from the tiny amount of googling I did it looks like the same form of cytosine was found in rat, mouse, and frog brains as early as 1972 (http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=1178489).

These are accurate comments.

Claiming this is a new Neucleotide is analagous to a situation in which there are only 4 types of bread in the world: Wholemeal, Rye, Pitta and Naan, and someone claims that they've discovered a new kind of bread called Wholemeal With Peanut Butter.

I think the key here is that differences is the genome as classically described are not the only factors in gene expression, the presence of other similar nucleotides can be responsible for the differing traits seen that cannot be explained through other genetic or environmental differences. Also if these nucleotides are not part of the classic genome, who knows how they are inherited and how we may be able to control the expression of traits spotted in the genome by applying these nucleotides. Sounds very interesting to me.

hey guys quit baggin on this intriguing discovery! yeah i would call leading the witness on this author for the wacky and wild claims of a new DNA base pair (ACGT... yeah girl you did do it). but its still cool that we may be uncovering how regulation might explain why humans are so different bananas even while we share a fair able amount of code! this is like where people are finding species differentiation cant be credited only towards sequence change. i just read different nuclear envelope pores help regulate genes in different human tissues. kinda on the same subject but look it up if you found this interesting :)