More than we think … a strange nitrogen base that makes up the genome of some viruses

The alphabet of life consists of 4 main letters that represent the nitrogenous bases that store an organism’s genetic code in DNA. These letters are: adenine, symbolized by the letter “A”, thiamine “T” (T), cytosine “C” (C), and guanine “G” (G).

One alphabet

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RNA, which is responsible for regulating the translation, transmission and decoding of genetic information, differs slightly from this rule, as it contains the nitrogenous base uracil (U) instead of thiamine.

The nitrogenous bases are specially coupled to be able to encode the genetic information and create the double strand of DNA. Adenine bonds to thiamine through two hydrogen bonds, while cytosine bonds to guanine through 3 hydrogen bonds.

Although this alphabet is sufficient for complex-celled organisms to store and express their genetic secrets, it seems that it is not sufficient for simple organisms.

Given the nature of the internecine warfare between viruses that infect bacteria – also known as phages – and their bacterial prey, both develop unique methods for eliminating the other. However, phages have taken this armed race to new levels of development.

Ambiguous phages

The story dates back to 1977, when scientists discovered that one of the phages – known as “Cyanophage S-2L” – had replaced all nitrogenous adenine bases with “2-aminoadinine” bases, which are coded by the symbol “Z. (Z). Hence, the alphabet of this virus contains the letters “ZTCG”.

And it seems that this modification that this type of phage introduces into its genetic material aims to provide itself with self-protection against bacteria. The nitrogenous base Z binds to thiamine through 3 hydrogen bonds – instead of two as adenine does – which means a stronger bond. Consequently, this gives the viral genome new characteristics, by making it more resistant to breakage if it is attacked by bacteria.

However, scientists have not detected any other phages that carry such a genetic modification as containing base Z (Z). Given the difficulty of culturing cyanophage S-2L in the laboratory, its genetic content has become a puzzle for scientists.

Therefore, we do not know much about how this nitrogen base is formed, as well as how it binds with thiamine to form dZ-DNA; Or what is known as the “Z-genome”.

Unique Genome-Z

Recently, the journal Science, in its April 30 issue , singled out 3 articles by independent research teams to answer these questions.

The first study conducted by Chinese researchers and the second by French researchers showed that there are two main proteins, “PurZ” and “PurB”, which are involved in forming the nitrogenous base “Z” (Z).

Whereas, the results of the third study conducted by an international team of scientists led by researchers from France confirmed these results and revealed an enzyme called “DpoZ”; Which is responsible for the binding and formation of the entire Z-genome.

By searching databases of gene sequences, the scientists discovered that there are many phages that contain gene sequences of genes similar to those that make up the aforementioned proteins and enzymes.

Of course, this new nitrogen base will provide more genetic diversity, which is what many scientists aspire to. Which can be likened to adding a new letter to your language that you speak, which means that there are new words that may be added to your language dictionary.

The same is true for a cell: the diversity of its letters means the production of a new component, the acquisition of a new function, etc. However, there are many questions we still don’t know about the Z-genome of these phages.

For example, is the Z-genome compatible with the natural cellular mechanisms found within our cells? Could it be used with the same approach that we are doing in artificial gene synthesis?