Friday, September 28, 2007


Organism of the Week

Okay, so it's time to write about something besides the hypocrisy of the Bush administration. Is there really any need to continue on about that after all this time? I try to resist, but sometimes it's just so breathtaking that I can't help myself.

Instead, I'm inaugurating a new feature that I hope to make a regular part of this weblog (not that there's anybody reading it, but what does that matter?), where I will describe and discuss some of the interesting features of an unusual, offbeat organism that I have come across in my work as a molecular biologist. Given that a lot of my work is in the field of DNA repair, it makes sense to start with the undisputed champion of putting a broken genome back together - Deinococcus radiodurans. It's a bacterium that can survive doses of ionizing radiation (the kind given off by radioactive decay and nuclear blasts) and ultraviolet radiation (the kind that gives you a sunburn) 500 times greater than those that would kill or severely injure a human being. Because natural sources of such high doses of radiation are exceedingly rare on earth, it's thought that these capabilities evolved not to counter the effects of radiation but rather to deal with extreme dehydration, which can also cause massive damage to DNA.

A new paper was published this week that describes some of the genetic features that make this organism so resistant to forces that cause severe damage to its DNA. For a long time, it was suspected that these organisms had unusual or highly efficient systems for DNA repair, or that the presence of multiple complete copies of the genome (usually more than four) present in the cell allowed for stitching the whole mess back together somehow after damage. But now, a consensus is developing that high manganese (Mn) levels in the cell, and correspondingly low levels of iron (Fe) serve to protect the regular DNA repair enzymes themselves from being damaged by reactive oxygen species (free radicals, e.g.) created by severe stresses such as high doses of radiation or extreme dehydration. The exact mechanism by which manganese helps protect proteins from damage remains to be investigated, but the new research on radiodurans makes it clear that it's not the damage to DNA itself that causes sensitivity to radiation, but rather damage to the proteins that are responsible for DNA repair, an unexpected and exciting finding.

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