© Adrian Sanborn, Erez Lieberman AidenPhysics simulation of 5 megabases of DNA forming loops and domains.
Most text books talk of four DNA bases. Later research has shown there to be five. No, wait, cross that out, there could be six. Scientists suggest that the methyl-adenine is the sixth base and that it is medically important.

DNA (deoxyribonucleic acid) is the main component of genetic material, found in humans and all other animals. DNA is formed by combining four parts or bases. These are coded A, C, G and T (representing adenine, cytosine, guanine and thymine).

The combination of these leads to thousands of possible sequences. This variation explains the genetic variability found across and throughout living creatures.

Use of the word base is historical, in reference to the chemical properties of 'nucleobases' in acid-base reactions; the term does not really describe their biological functions.

There are, in addition to the four main bases, two other bases. These are methylated forms of other DNA bases. Methylation is a form of alkylation with a methyl group. These have epigenetic implications. Epigenetics is essentially additional information layered on top of the sequence of letters that makes up DNA.

A fifth base was identified a few years ago. Called methyl-cytosine (mC), this is derived from cytosine. The find was of significance because mC can switch genes on or off depending on the physiological needs of each tissue. There is a probable link between alterations to this base and the risk of developing cancer.

Now comes the news, via the University of Barcelona, that there could be a sixth base: methyl-adenine (mA). This base could be key in the life of the cells. The base was identified using advanced screening methods.

In terms of the significance of this base, methyl-adenine appears to regulate the expression of certain genes in eukaryotic cells. This means that it could have a key role in stem cells and in early stages of animal development. Further research will be required to determine the full significance and whether this base is commonly found in humans.

The description of the sixth base has been detailed in the journal Cell. The science paper is called "An Adenine Code for DNA: A Second Life for N6-Methyladenine."