In biology class you learned that DNA (deoxyribonucleic acid) is the main component of our genetic material and it is formed by combining four parts: A, C, G and T (adenine, cytosine, guanine and thymine), called bases of DNA. These bases combine in thousands of possible sequences to provide the genetic variability that enables the wealth of aspects and functions of living beings.

In the early 1980s, the four "classic" bases of DNA sort of got a fifth - methyl-cytosine (mC), derived from cytosine, which was later linked to epigenetic mechanisms because it is able to switch genes on or off depending on the physiological needs of each tissue.

Now there may be a sixth. Manel Esteller, director of the Epigenetics and Cancer Biology Program of the Bellvitge Biomedical Research Institute (IDIBELL), ICREA researcher and Professor of Genetics at the University of Barcelona, describes the possible existence of methyl-adenine (mA), which also helps determine the epigenome and would therefore be key in the life of the cells.

"It was known for years that bacteria, evolutionarily very distant living organisms of us, had mA in its genome with a protective function against the insertion of genetic material from other organisms. But it was believed that this was a phenomenon of primitive cells and it was very static" says Manel Esteller. "However, this issue of CELL publishes three papers suggesting that more complex cells called eukaryotes such as the human body cells, also present the sixth DNA base. These studies suggest that algae, worms and flies possess mA and it acts to regulate the expression of certain genes, thus constituting a new epigenetic mark. This work has been possible thanks to the development of analytical methods with high sensitivity because levels of mA in described genomes are low. In addition it seems that mA would play a specific role in stem cells and early stages of development, "explains the researcher.

"Now the challenge we face is to confirm this data and find out whether mammals, including humans, we also have this sixth DNA base, and consider what its role is."

Citation: Heyn H, Esteller M. An Adenine Code for DNA: A Second Life for N6-Methyladenine. Cell (2015). DOI:10.1016/j.cell.2015.04.021