Friday, May 15, 2009

Laser Protein Flashlight Blackout!

The weird pyramid you see in this movie is a cluster of DNA, about 1 % of a millimeter in diameter. The DNA itself is invisible (black), but it's coated with thousands of fluorescent DNA-binding proteins that I genetically engineered. You can think of these proteins as each having a tiny little flashlight; when they all bind to the DNA, they make it shine bright white. A second or so into the film, I zap the top region of the cluster with a highly focused laser beam. The proteins are still there, but the laser permanently disables their flashlights, resulting in a blackout over the zapped region:

You'll notice that this blackout is quite short - in fact, it's more like a brownout. How are the flashlights returning? The key is to understand that these flashlight-bearing proteins are not permanently bound to DNA. They are constantly coming on and off, too fast for the eye to see. In our case, the zapped proteins with dead flashlights are quickly being replaced by fresh proteins with functional flashlights. Using this method, we can measure the on/off rate of these proteins on DNA. This graph tracks the brightness of a zapped (blue) and an unzapped (olive) region over time; it takes about 30 seconds to fully replace all the proteins in the zapped region:

Your body may look stable, but experiments like this demonstrate that there is constant motion inside every cell, much faster than the eye can see. These experiments are also really fun because you get to fire a laser at a cell - it's kind of like playing a video game, only tinier and real.


:) said...
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Yael said...

Now I'm really curious what your research is about!