Tuesday, May 04, 2021

Is S-2L the future of viruses?

This is kind of fascinating, in a geeky kind of way.

You may (or may not) know that pretty much all life on Earth employs the same four nucleotides in its DNA: adenine (A), thymine (T), cytosine (C) and guanine (G), and all the genes that make life as we know it tick are made up of long strings of these organic molecules. This creates the familiar (or maybe not so familiar) genetic alphabet ATCG.

I say "pretty much all life on Earth" advisedly, because, since 1977, scientists have been aware of a specific bacteriophage (a virus that attacks bacteria), with the unassuming monicker S-2L, that turns this rule on its head. This DNA virus cyanophage has evolved to substitute all instances of adenine with 2-aminoadenine (also known as 2,6-diaminopurine), which has been given the alphabetic label Z for some reason, yielding a ZTCG genetic alphabet.

Why this originally developed is not certain, but is thought that it is just a new tactic in the ongoing war between viruses and bacteria, effectively taking the arms race to a new level. The Z base forms a triple bond to the opposite T base on the "rungs" of the DNA ladder (as opposed to the double bonds in the usual ACTG-type DNA), making it stronger and more difficult for the bacteria to prise apart and destroy.

S-2L was long thought to be an anomaly, just one of those random things that nature throws at us from time to time, like duck-billed platypuses, octopuses and black holes. But turns out that it is not so unusual after all. Three separate studes from France and China have shown that there are actually a whole army of Z-genome bacteriophages out there, and identified the proteins and enzymes involved in their assembly.

Of course, we are only beginning to speculate on what it might all mean for us and the living world that we know. I just hope that COVID-19 doesn't find out about it; otherwise we are cooked!

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