Our little diva (from a small town in southern Iceland)

25 May 2013 by Kerstin Hoppenhaus, posted in Ancient DNA, Genetics

Photo: Zach Klein (http://www.zachklein.com/)


Enzymes are reliable and indispensable workhorses in every cell. Without them, things would happen very slowly or not at all. Molecular biologists use them as tools as routinely as pipettes, vortexers, centrifuges – automatically, no fuss.

So I was a bit surprised, when Marie referred to one of her enzymes as „our little diva“.

The „diva“ officially goes by the name of CircLigaseTM II ssDNA Ligase, and for an enzyme she really is quite demanding. For one, she doesn’t take well to the vortexer, but has to be stirred by hand. Instead of magnesium-kations like most, she prefers manganese. And while most enzymes will perform perpetually as long as there is enough „food“ around, this one actually „tires“ over time. On top of that, maybe not surprisingly, she is prohibitively expensive. But since she also is the only enzyme commercially available to operate on single-strand DNA, people are willing to put up with her capricious nature. „It took us a while, though“, Marie says. „I have been doing nothing but ligation experiments for months!“

Now, the protocol works, and the CircLigase has a key role in it. She induces adapters to bind to the ends of the DNA-strands. Without adapters, the strands would be useless. Unintelligable gibberish in buffer soup.

In the 1990s, the thermophile bacterium Thermus scotoductus was isolated from „a hot water pipeline in a small town in southern Iceland“. Thermus is a large genus of bacteria, ranging from the geysirs of Yellowstone to Japanese hot springs to the depths of Tanganyika Lake in Africa, and a well-known source of heat-resistant enzymes for molecular biologists.

Thermus scotoductus has a parasite, the bacteriophage TS2126. Like its host, the phage is thermophile and can survive at high temperatures. So can its enzymes. Including its ligases.

In bacteria, ligases, among other things, fix broken strands of DNA. In phages, they induce phage-DNA to become circular once it enters the host, to avoid detection by the host’s defenses.

It usually makes the circles by binding the DNA-strand’s 3’-end to the 5’-end. But since in this case Marie a step before has trimmed away the phosphates, the ligase cannot go about its normal business. And instead of sulking in its corner, it grabs the next best thing to attach to the ends, which thanks to Marie’s careful manipilation happens to be the desired adapter.

Not so bad for a little diva.

Maybe she really is a little Icelandic elf helping us to come to grips with the traces of our ancient past...



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