Abstract
BackgroundA variety of strategies for survival of UV irradiation are used by cells, ranging from repair of UV-damaged DNA, cell cycle arrest, tolerance of unrepaired UV photoproducts, and shielding from UV light. Some of these responses involve UV-inducible genes, including the SOS response in bacteria and an array of genes in eukaryotes. To address the mechanisms used in the third branch of life, we have studied the model archaeon, Halobacterium sp. strain NRC-1, which tolerates high levels of solar radiation in its natural hypersaline environment.ResultsCells were irradiated with 30–70 J/m2 UV-C and an immunoassay showed that the resulting DNA damage was largely repaired within 3 hours in the dark. Under such conditions, transcriptional profiling showed the most strongly up-regulated gene was radA1, the archaeal homolog of rad51/recA, which was induced 7-fold. Additional genes involved in homologous recombination, such as arj1 (recJ-like exonuclease), dbp (eukaryote-like DNA binding protein of the superfamily I DNA and RNA helicases), and rfa3 (replication protein A complex), as well as nrdJ, encoding for cobalamin-dependent ribonucleotide reductase involved in DNA metabolism, were also significantly induced in one or more of our experimental conditions. Neither prokaryotic nor eukaryotic excision repair gene homologs were induced and there was no evidence of an SOS-like response.ConclusionThese results show that homologous recombination plays an important role in the cellular response of Halobacterium sp. NRC-1 to UV damage. Homologous recombination may permit rescue of stalled replication forks, and/or facilitate recombinational repair. In either case, this provides a mechanism for the observed high-frequency recombination among natural populations of halophilic archaea.
Highlights
A variety of strategies for survival of UV irradiation are used by cells, ranging from repair of UV-damaged DNA, cell cycle arrest, tolerance of unrepaired UV photoproducts, and shielding from UV light
In order to understand gene expression responses to UV at the whole genome level, we studied the model archaeon, Halobacterium sp. strain NRC-1, employing DNA microarrays
Together with our studies of the physiological response of a model archaeon, has shown that genes involved in homologous recombination are induced by UV irradiation in relatively low doses
Summary
A variety of strategies for survival of UV irradiation are used by cells, ranging from repair of UV-damaged DNA, cell cycle arrest, tolerance of unrepaired UV photoproducts, and shielding from UV light. Some of these responses involve UV-inducible genes, including the SOS response in bacteria and an array of genes in eukaryotes. Saline Systems 2005, 1:3 http://www.salinesystems.org/content/1/1/3 in response to UV-damage including several DNA repair genes, no eukaryotic equivalent of the bacterial SOS response has been identified [2]. The classic SOS response system regulated by LexA is lacking in archaea, and the relationship between the bacterial and eukaryotic repair systems in archaea is not currently known [9]
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