The operon of species is highly induced upon UV stress. assays

The operon of species is highly induced upon UV stress. assays indicated that nicks UV-damaged DNA. In addition, RecQ-like helicase Saci_1500 is able to unwind homologous recombination intermediates, such as Holliday junctions. Interestingly, a deletion mutant was more sensitive to UV light but not to the replication-stalling agents hydroxyurea and methyl methanesulfonate, suggesting that Saci_1500 functions specifically in the UV damage pathway. Together these results suggest a role of Saci_1497 to Saci_1500 in the repair or transfer of DNA that takes place after UV-induced damage to the genomic DNA of species increase their fitness after UV stress by a UV-inducible pilus system that enables high rates of DNA exchange Rabbit polyclonal to TIGD5 between cells. Downstream of the pilus operon, three genes that seem to Pluripotin play a role in the repair or transfer of the DNA between cells were identified, and their possible functions are discussed. Next to the previously described role of UV-inducible pili in the exchange of DNA, we have thereby increased our knowledge of DNA transfer at the level of DNA processing. This paper therefore contributes to the overall understanding of the DNA exchange mechanism among cells. INTRODUCTION In all domains of life, DNA repair is crucial for maintenance of genome integrity upon exposure to intra- or extracellular DNA-damaging threats (1). Unlike DNA repair in bacteria, archaeal DNA repair and its regulation are still far from well understood (1, 2). Homology searches revealed that the proteins in archaeal DNA repair pathways show similarities to both bacterial and eukaryotic proteins. In addition, DNA Pluripotin repair proteins with unique archaeal features exist (3). Previously, it was speculated that archaea might have SOS-like responses similar to those in certain bacteria (4); Pluripotin however, microarray studies revealed that neither (5, 6) nor species (7, 8) show a strong induction of genes involved in excision repair upon UV-induced DNA damage. The only archaeal DNA repair genes upregulated in response to UV light are implicated to play a Pluripotin role in homologous recombination (HR), a pathway involved in double-strand break (DSB) repair (5,C8). For hyperthermophilic organisms such as are similar to those observed in mesophilic organisms (10). Thus, efficient DNA repair systems that might involve efficient HR mechanisms seem to be present in hyperthermophilic archaea. UV light is one of the most important causes of DNA damage in cells from all domains on Earth. It is accountable for direct DNA lesions, such as cyclobutane pyrimidine dimers (CPDs), hydrated pyrimidines, and pyrimidine-pyrimidine photoproducts, as well as for indirect lesions, such as DSBs (11). In cells are predominantly present in G2 phase (18), most of the time there is a second copy of the chromosome to repair DSBs via HR. However, in Pluripotin G1 phase or upon severe DNA damage, HR might not be possible, and unrepaired DSBs become lethal. cells exchange DNA in a UV-inducible manner (7, 19, 20). This process is mediated by cellular aggregation, in which UV-inducible pili (pili) play an essential role (21, 22). It was shown that transferred DNA can be used as a template for HR (19). Importantly, upon UV induction, strains that have the ability to exchange DNA show significantly higher survival rates than strains that do not (19). Given the DNA-damaging properties of UV light and because the DNA-damaging agent bleomycin also induces cellular aggregation (19), we assume that the transfer of DNA between cells is involved in DSB repair in a recombinational manner. Downstream of the gene cluster encoding the pili, four conserved genes are present. These genes encode a predicted endonuclease III (EndoIII; Saci_1497), a ParB-like nuclease (Saci_1498), a glycosyltransferase (Saci_1499), and a DNA helicase (Saci_1500) (Fig. 1). Given the putative DNA processing functions of three of these proteins, we hypothesized that they are involved in the DNA transfer or homologous recombination taking place as soon as DNA is transferred. Here, we therefore studied Saci_1497 to Saci_1500 and their roles in the DNA repair taking place subsequent to the formation of UV-induced DNA damage. Our results show a clear link between these genes and UV-damaged DNA repair and suggest a role of the individual genes in the DNA damage response or homologous recombination. Similar to the SOS response in certain bacteria, the system in combination with homologous recombination might rescue cells from DNA-damaging threats. FIG 1 Schematic overview of the gene cluster and its downstream genes in different members of the strains MW001 (23), MR31 (24), and JDS183 (25) and mutants derived from those strains (Table 1) were grown aerobically at 75C in basic Brock medium (26) supplemented with 0.1% enzymatic digest of casein (N-Z-Amine), 0.2% dextrin, and 10 g/ml uracil and adjusted to pH 3.5 with sulfuric acid. For plates with solid medium, the medium was supplemented with 0.6% Gelrite polymer, 3 mM CaCl2, and 10.