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.
The word “base” is commonly used to reference chemical properties of what are more accurately known as “nucleobases” ( as in acid-base reactions). This is considered outmoded today because the notation does not indicated the 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 two other bases have epigenetic implications. Epigenetics refers to further information layered on top of DNA’s sequence of letters, acting as external modifications to DNA that turn genes “on” or “off.” These modifications do not change the DNA sequence; however they affect how cells “read” genes.
To give an example, as mentioned by Live Science: “epigenetics is the reason why a skin cell looks different from a brain cell or a muscle cell. All three cells contain the same DNA, but their genes are expressed differently (turned “on” or “off”), which creates the different cell types.”
A fifth base was identified a few years ago. This was named methyl-cytosine (mC), this is derived from cytosine. The find was regarded as important 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. If the base is identified, then the significance will need to be determined.
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.”