Transcriptional responses to biologically relevant doses of UV-B radiation in the model archaeon, Halobacterium sp. NRC-1
Most studies of the transcriptional response to UV radiation in living cells have used UV doses that are much higher than those encountered in the natural environment, and most focus on short-wave UV (UV-C) at 254 nm, a wavelength that never reaches the Earth's surface. We have studied the transcriptional response of the sunlight-tolerant model archaeon, Halobacterium sp.
NRC-1, to low doses of mid-wave UV (UV-B) to assess its response to UV radiation that is likely to be more biologically relevant.
Results: Halobacterium NRC-1 cells were irradiated with UV-B at doses equivalent to 30 J.m-2 and 5 J.m -2 of UV-C.
Transcriptional profiling showed that only 12 genes were up-regulated 1.5-fold or more by both UV-B doses. The most strongly up-regulated gene was radA1 (vng2473), the archaeal homologue of RAD51/recA.
The others included arj1 (vng779) (recJ-like exonuclease), top6A (vng884) and top6B (vng885) (coding for topoisomerase VI subunits), and nrdJ (vng1644), which encodes a subunit of ribonucleotide reductase. We have found that five of the consistently UV-B up-regulated genes, radA1 (vng2473), vng17, top6B (vng885), vng280 and npa (vng6361), share a common 11-base pair motif in their promoter region, TTT(C/T)ACTTTCA.
The same sequence was found in radA promoters in other halophilic archaea, as well as in the radA promoter of Methanospirillum hungatei. We analysed the transcriptional response of a repair-deficient uvrA (vng2636) uvrC (vng2381) double-deletion mutant and found little difference between it and the response in repair proficient cells.
Conclusions: Our results show only a few genes consistently up-regulated after exposure to UV-B light at low, biologically relevant doses.
Twelve genes were up-regulated after both UV-B doses, and only four genes were up-regulated by all doses of UV-B and UV-C that we have used in this work and previously. These results suggest that high doses of UV-C radiation do not necessarily provide a good model for the natural response to environmental UV.
We have found an 11-base pair motif upstream of the TATA box in five of the UV-B up-regulated genes and suggest that this motif is the binding site for a transcriptional regulator involved in their response to UV damage in this model archaeon.
Author: Ivan Boubriak, Wooi L Ng, Priya DasSarma, Shiladitya DasSarma, David J Crowley and Shirley J McCready
Credits/Source: Saline Systems 2008, 4:13
Published on: 2008-08-29
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