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Thursday, August 23, 2012

The Yeasty Boys

"Enthusiasm is the yeast that rises the dough"
Paul J.  Meyer

Carl Zimmer describes how our distant cousin, yeast, has been used to discover a tumor shrinking drug.

In health physics we used yeast as an aid in understanding that the genes employed to resist ionizing radiation are different than those used to resist the more common damage of metabolism called metabolic oxidative damage (MOD).  This is illustrated here (where "IR" stands for ionizing radiation, and H2O2 stands for hydrogen peroxide, one of the oxidizers).

Of course this is not surprising because the type and location of IR damage is different than MOD as are the cellular repair mechanisms.  This was discussed here - "DNA Damage & Repair".


  1. What the top Venn diagram shows is that the genes employed are indeed largely the same against both types of damage. It shows that about 97% of the genes activated to counter IR are also genes found active against H2O2,(298+150+8)/470.

    The bottom diagram is not a Venn diagram, despite its billing, so the numbers there are valueless.

  2. Well if you want to interpret that way, go ahead. The top Venn shows the gene sharing with one study by 158/470 = 34% in which IR required 470 genes total and the other 260 total a difference of 55%. In the second study there was 448/470 = 95%, but a total of 525 genes used for H2O2, a difference of 12%.

    Not in diagram, but in text, is the finding that of the top 100 genes conferring resistance to IR, only 35 were in the top 100 that were sensitive to H2O2.

    Oxidants mostly cause protein damage in the mitochondria, whereas the IR effect of concern is DNA damage in the nucleus. Yeast has a lower ratio of proteins/DNA than humans, so we expect that it represents a very low estimate of what occurs in humans.

    The numbers in the lower Venn diagram are not valueless. They show relationships between other oxidizers and IR.