1. Expression of Double-Strand Break Repair Genes in Deinococcus radiodurans
Under Oxidative Stress
By David Johanson under the mentorship of Jeffery Dunmire
Abstract
Deinococcus radiodurans is an extremely hardy species of bacteria that can survive
environmental conditions that would kill almost all other life. Studies before have shown that
certain characterized and uncharacterized proteins experience increased mRNA transcription
levels when exposed to reactive oxygen species and UV radiation from 400 to 200nm. Three
genes in particular were assayed using Real-Time PCR to determine their transcription levels in
early to mid recovery phase after exposure to UVA radiation and hydrogen peroxide. They were
recA, ddrB, and GAP. Original expectations were that the genes for RecA and DdrB proteins
would experience increased transcription levels when exposed to UVA radiation and hydrogen
peroxide through RT-PCR of their mRNA. GAP was also assayed because it was previously
established as a housekeeping gene for D. radiodurans in a similar experiment (Tanaka et al
2004). Results were both expected and unexpected. When exposed to hydrogen peroxide, genes
for GAP, RecA, and DdrB each experienced higher transcription levels that control groups. Yet
all three genes also experienced equal or lower transcription levels when exposed to UVA
radiation. Most notable were transcriptional levels for GAP. When exposed to hydrogen
peroxide, the fold change for GAP expression was at about 4.84, but at about 0.167 when
exposed to UVA radiation. Being a housekeeping gene, changes as dramatic as these are the
opposite of what is expected. Further discussion of results will be carried on in the Discussion.