Sixth DNA base discovered?

When DNA is replicated, methyl-cytosine pairs with guanine just like cytosine does. The only way to maintain the 'methylation marks' is to add a methyl group back on to the newly synthesized cytosine. When DNA is converted into RNA, which is then converted into protein, whether a cytosine has a methyl group attached makes no difference to the final protein.

So whether a cytosine is methylated or not doesn't change the DNA sequence you inherit from your parents. It doesn't change the structure of the protein produced from that gene. What it can do, is change when and where that gene is expressed - which can make a huge difference to the behaviour of the cell.

For instance, a gene such as BRCA1 could be 'turned off' because too many cytosines are methylated, and this could cause a cell to become cancerous. Or a lack of methylation could cause too much c-Myc to be produced, which could result in the same outcome. But then, there many other genetic regulatory mechanisms that can do that as well - such as histone modifications, chromatin structure, transcription factors, and probably methyl-adenine too! All these mechanisms interact to ensure genes are turned on and off at the right time and place, and this field is known as 'epigenetics'.

Methyl-cytosine is a modified version of cytosine that is a very important part of epigenetics, but since it is almost irrelevant to other aspects of genetics, I would argue that you could not consider it a 'fifth base'. Having read the paper, methyl-adenine is the same - interesting new aspect of epigenetics and gene regulation, but not a new base. Also, this paper doesn't exactly 'discover' it, we found methyl-adenine in bacteria in the 60s....

If you want to read about truly new bases, scientists actually synthesised an entirely new pair of bases last year, that can replicate and encode RNA and proteins! A seriously cool step forward in synthetic life http://www.nature.com/news/first-life-with-alien-dna-1.15179

I kind of cringed when I read that they are "fifth" and "sixth" base pairs because of the significant functional overlap with two of the existing ones.

I think the 'layperson' summary of this article should be that the authors may have found an unappreciated mechanism for gene expression [1-3; 3 articles were published simultaneously].

As you may have heard, your genome comprises four 'letters', called the DNA bases. Collections of these bases called genes encode proteins, molecular structures that perform myriad functions. Indeed, everything that you can see on a living organism is either protein or was created by a protein.

Genes have specific functions that are often limited in both time and space - the protein encoded by a gene may only be needed in the embryonic pancreas, for example. In the field of epigenetics, researchers try to understand the causes of this tight control of gene activity, among other things.

The addition of methyl groups to DNA bases is a long appreciated way to control gene activity - see ref. 4, which is an excellent, freely available cell biology text. The DNA base cytosine is often modified to yield methyl-cytosine, a methylated base with a well established role in the regulation of gene expression; methyl-cytosine tends to mark genome areas with lower probabilities of gene expression.

The authors find that methyl-adenine seems to play a role opposite to methyl-cytosine, surprisingly. While the existence of methyl-adenine was known in bacteria, its function in gene expression in more complicated organisms was not known. Refs 1-3 don't show a causative role for methyl-adenine in increasing gene expression but the correlations the authors report are likely to be followed up.

In summary, the story behind this article is pretty exciting and could indeed expand our understanding of epigenetics, cell biology and perhaps more.

One should remain extremely skeptical of anything in Science Daily - always go to the source.

[1] http://www.sciencedirect.com/science/article/pii/S0092867415...

[2] http://www.sciencedirect.com/science/article/pii/S0092867415...

[3] http://www.sciencedirect.com/science/article/pii/S0092867415...

[4] http://www.ncbi.nlm.nih.gov/books/NBK26854/

How many blood types are there? Most people will say 4 (or 3, or 2 depending on how you define it). But there are actually far more of them, but the rest are rare or less important.