…2-aminoadenine, and if you happen to be a bacteriophage it’s quite important.
Very important, in fact. And it might be important to our understanding of, well, how life even works.
Most life on Earth has DNA (the exception is some viruses, which use RNA instead. SARS-CoV-2 is an RNA virus.).
And DNA contains four bases. Adenine, cytosine, guanine, and thymine. All DNA has these four bases, and they bond together in specific ways. Those specific ways make up the genome, the biological code that makes us us.
Until they don’t.
In 1977, researchers discovered that a bacteriophage (a kind of virus that infects bacteria) called cyanophage S-2L was…well…interesting. Instead of adenine, it had 2-aminoadenine (or 2,6-diaminopurine, I’m seeing both). They added this to the DNA alphabet as Z, but the virus was hard to culture. They thought this was some one off weirdness that had no doubt evolved as host evasion. Bacteria mutate quickly, so phages have to keep up, and it was unsurprising something really weird would happen.
S-2L Is Not Alone
Except, it wasn’t. Three separate papers have shown that the Z-genome is, in fact, not all that uncommon in bacteriophages. The theory is that it is a defense mechanism against the bacterial immune system, which uses nucleases to tear viruses apart. The Z base forms an extra bond to the opposing T base, making the entire genome more stable.
Presumably it’s only an advantage in this specific situation as we have not found it in anything other than a bacteriophage. Perhaps it’s a disadvantage in other situations. Most likely, it’s actually too stable, slowing mutation rates and making sexual reproduction harder.
(This is, btw, not quite the same thing as Z-DNA, which is left handed DNA that winds to the left, not the right, and is in everything including us).
The Z-genome appears to have existed since the early days of life on our planet. And it has also been found in at least one legitimate meteorite.
Heck, maybe these bacteriophages are alien life on our very own planet. Or maybe I’m just obsessed with aliens. Or maybe it’s the other way around; maybe the Z-genome came first and the A-genome came later and beat it up, leaving these bacteriophages as the last remnant.
Is This Useful?
So, is this just a curiosity or is it useful? It’s actually highly useful.
Now we know how the Z-genome is made (it involves various proteins and enzymes), we can make it ourselves. This might be used to improve phage therapy, which is an alternative to antibiotics. It could be used to make artificial DNA more stable, making gene therapy easier.
And it adds to our understanding about how genetics work and I, for one, find that fascinating.
Even if they aren’t aliens.