Oligotrophic (sub-)tropical oceans receive intense incident ultraviolet radiation (UV, 280–400 nm) and their water columns are highly transparent due to their nutrient-deficient state. This combination suggests a high potential for adverse effects on organisms, yet only few reports describe the UV exposures received in these waters and the associated impacts on marine biota. Here, we aimed to investigate the UV bio-optics of various open ocean locations and, using the Red Sea as a representative oligotrophic environment, we investigated the pattern of UV attenuation over a wide latitudinal range, quantified UV exposures in the water column, and determined impacts of UVB (280–320 nm) on indigenous phytoplankton and scleractinian corals. Globally, the lowest average downwelling diffuse attenuation coefficients (Kd) in the UV spectrum were recorded in the ultra-oligotrophic Indian Ocean Subtropical Gyre (Kd(313nm): 0.110 m-1) and South Pacific Gyre (Kd(313nm): 0.098 m-1), while aCDOM(λ) was ~1–2 orders of magnitude higher than ap(λ), In the Red Sea, UV attenuation mirrored the prevailing latitudinal gradient in nutrients, with the lowest and highest Kd(313) of 0.130 m-1 and 0.357 m-1 measured in the far north and in the south of the basin, respectively. Central Red Sea waters were most transparent to UV in late summer, i.e., a few weeks after incident irradiances and SSTs reach their annual maximum. Although, the projected increase of SST due to climate change means that extreme UV exposure and temperatures could coincide in the near future. This finding is of particular relevance since we found that Red Sea diatom species such as C. closterium are highly sensitive to UVB-induced photoinhibition and cell decay (LRD50: 11.4 kJ). Water temperature also governed the UVB sensitivity of Synechococcus sp., although this group exhibited a high resistance overall (LRD50: 57 kJ to non-detectable). For corals, we found that UVB-removal generally had little impact on the oxidative stress levels and photophysiology of S. pistillata and P. verrucosa from shallow waters, but considerably accelerated the acclimation of upward transplanted corals, which highlights that UVB is a crucial stressor that governs the photoacclimation capacity of Red Sea corals.

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Copepods in high elevation lakes and ponds in Colorado are exposed to significant levels of ultraviolet radiation (UV), necessitating development of UV avoidance behavior and photoprotective physiological adaptations. The copepods are brightly pigmented due to accumulation of astaxanthin, a carotenoid which has photoprotective and antioxidant properties. Astaxanthin interacts with a crustacyanin-like protein, shifting its absorbance from 473 nm (hydrophobic free form, appears red) to 632 nm (protein-bound complex, appears blue). In six sites in Colorado, habitat-specific coloration patterns related to carotenoprotein complex have been observed. The objective of this study was to determine whether pigment accumulation or carotenoprotein expression has a greater effect on resistance to UV exposure. For each site, copepod tolerance to UV was assessed by survivorship during UV exposure trials. Average UV exposure was determined for each habitat. Astaxanthin profiles were generated for copepods in each site. Ability to withstand UV exposure during exposure trials was significantly different between color morphs (p < 0.0001). Red copepods were found to tolerate 2-fold greater levels of UVB than blue or mixed copepods. Additionally, red copepods have much higher levels of total astaxanthin than blue or mixed copepods (p < 0.0001) and receive a higher daily UV dose (p < 0.0003). Diaptomid carotenoprotein sequence is not homologous with that of other crustaceans in which crustacyanin has been characterized which prevented quantification of carotenoprotein transcript expression. Overall, diaptomid color morph may be an important indicator of UV conditions in high elevation lentic ecosystems.

Following low levels of UV exposure, Escherichia coli cells deficient in nucleotide excision repair recover and synthesize DNA at near wild type levels, an observation that formed the basis of the post replication recombination repair model. In this study, we characterized the DNA synthesis that occurs following UV-irradiation in the absence of nucleotide excision repair and show that although this synthesis resumes at near wild type levels, it is coincident with a high degree of cell death. We confirm that the replication occurring under these conditions involves extensive levels of strand exchange. However, cells undergoing this form of replication accumulate strand exchange intermediates that fail to resolve into discrete molecules, resulting in grossly filamentous, multinucleate cells. Taken together the results demonstrate that the DNA synthesis that occurs in UV-irradiated nucleotide excision repair mutants is aberrant and suggests that post replication repair is not an efficient mechanism to promote survival in the absence of nucleotide excision repair. The role that nucleotide excision repair plays in the recovery of replication following UV-induced DNA damage was further characterized by examining the specific role of UvrD in processing and restoring UV-arrested replication forks. UvrD is a helicase with functions associated with nucleotide excision repair and replication. UvrD catalyzes the removal of the damaged region by nucleotide excision repair proteins and removes the stretch of DNA incised during methyl-directed mismatch repair during replication. Recent biochemical studies have led to the proposal that UvrD may promote fork regression and facilitate resetting of the replication fork following arrest. However, the molecular activity of UvrD at replication forks in vivo has not been directly examined. In this study, we show that UvrD is required for DNA synthesis to recover. However, in the absence of UvrD, the displacement and partial degradation of the nascent DNA at the arrested fork occurs normally. In addition, damage-induced replication intermediates persist and accumulate in uvrD mutants in a manner that is similar to that observed in other nucleotide excision repair mutants. These data indicate that following arrest by DNA damage, UvrD is not required to catalyze fork regression in vivo and suggest that the failure of uvrD mutants to restore DNA synthesis following UV-induced arrest relates to its role in nucleotide excision repair.

Turmeric polar extract (TPE) was obtained by dielectric-precipitation of turmeric slurry and found to contain three proteins with two in the 10-11 KDa range being dominant. Antioxidative activity and persistence (AP) of TPE (5%, w/v) respectively showed 87% and 85% greater generation of alkoxy- and peroxyl radicals compared the non-redox-active buffer alone showing significant (p<0.05) pro-oxidative behavior. Conversely, purified curcumin (CU) (0.1% w/v) was dramatically antioxidative with AA and AP values of 2,828 and 1,129%, respectively, compared to the blank. However, a combination of the two at the same concentration dropped these values to 590 and 389%, respectively, reflecting dramatic dampening of the efficacy of CU. Ultraviolet radiation significantly modulated the efficacy of CU where UVB (300 nm) exposure gave the highest enhancement when limited to five min. Data showed that turmeric contains highly pro-oxidant polar proteins that significantly dramatically diminishes the beneficial antioxidative efficacy of its principal phytochemical, CU.

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<p>  </p> <p>Cyanobacteria are among the simplest organisms to display circadian rhythms that synchronize endogenous physiological activities with a ~12-hour-light:12-hour-dark (12L:12D) cycle of the external environment. Detected by the input pathway composed of CikA and LdpA proteins, light is transduced to the central circadian oscillator encoded by the gene cluster <em>kaiABC. </em>While KaiC phosphorylation is primarily regulated by KaiA and KaiB proteins, two key components of the output pathway, RpaA and SasA proteins, mediate between KaiC phosphorylation, genome-wide expression, and control of cell division. In this study, <em>Synechococcus elongatus </em>UTEX 2973 showed similar growth patterns when subjected to white light only and white light supplemented with ultraviolet A (UV-A) radiation under 12L:12D intervals, although UV-A radiation hindered growth during light periods. Under continuous illumination, growth rates of <em>S. elongatus </em>UTEX 2973 were reduced by UV-A radiation but reflected intrinsic circadian rhythmicity. To elucidate the critical role of the circadian clock, a mutant void of <em>kaiABC</em> was generated via the CRISPR/Cpf1 system. A dysfunctional clock severely disrupted inherent growth rhythmicity, which was exacerbated by UV-A radiation. To investigate the effects of UV-A radiation on transcription patterns in <em>S. elongatus </em>UTEX 2973, expression levels of circadian genes, specifically <em>kaiABC</em>, <em>cikA</em>, <em>lpdA</em>, <em>rpaA</em>, and <em>sasA</em>, were assessed by qPCR analysis. For the UV-A-treated wild-type strain, <em>kaiA</em> and <em>kaiB</em> expression was generally downregulated, <em>kaiC</em> expression was upregulated during the second dark period, and <em>rpaA</em> expression was either upregulated or downregulated depending on the period. For the UV-A-treated Δ<em>kaiABC </em>strain, <em>lpaA</em> expression was upregulated in darkness, whereas <em>rpaA</em> and <em>sasA</em> expression was downregulated during light periods. When Δ<em>kaiABC </em>and wild-type strains were examined in the presence and absence of UV-A radiation, expression of <em>lpaA</em>, <em>rpaA</em>, and <em>sasA</em> was universally downregulated, yet <em>cikA</em> expression was upregulated in the dark. This study was the first to evaluate the impact of UV-A radiation on cyanobacterial circadian rhythms, in which UV-A radiation negatively affected cyanobacterial growth and strongly altered gene expression patterns over time. Without the circadian clock, rhythmicity of growth and transcription was demolished, such that the consequences were aggravated for the output pathway that relayed signals downstream from the central oscillator. </p>

No description available.

No description available.

DNA mismatch repair (MMR) recognizes and repairs bases incorrectly incorporated during DNA replication. Germ line mutations in two MMR genes, namely hMSH2 and hMLHl, account for approximately 98% of hereditary non-polyposis colorectal cancers. There is conflicting evidence for the role of hMLHl and hMSH2 in the transcription-coupled repair (TCR) pathway of nucleotide excision repair (NER). Here we have examined the role of these MMR genes in NER using two reporter gene assays. AdHCMVlacZ is a replication-deficient recombinant adenovirus that expresses the B-galactosidase reporter gene under the control of the human cytomegalovirus (HCMV) immediate-early promoter. We have reported a reduced host cell reactivation (HCR) for B-galactosidase expression of UVC-irradiated AdHCMVlacZ in TCRdeficient Cockayne syndrome (CS) fibroblasts compared with normal fibroblasts, indicating that HCR depends, at least in part, on TCR. In addition, we have reported that UVC-enhanced expression of the undamaged reporter gene is induced at lower UVC fluences to cells and at higher levels after low UVC fluences in TCR-deficient compared with normal human fibroblasts, suggesting that persistent damage in active genes triggers increased activity f~om the HCMV-driven reporter construct. We have examined HCR and UV-enhanced expression of the reporter gene in hMLHl-deficient HCT116 human colon adenocarcinoma cells and HCT116-chr3 cells (the MMR-proficient counterpart of HCT116) as well as hMSH2-deficient LoVo human colon adenocarcinoma cells and their hMSH2-proficient counterpart SW 480 cells. We show a greater UV -enhanced expression of the undamaged reporter gene after low UVC exposure in HCT116 compared with HCT 116-chr3 cells ;md in Lo Vo compared with SW 480 cells. We show also a reduced HCR in HCT 116 compared with HCT 116-chr3 cells and in Lo Vo compared with SW 480 cells. However, the reduction in HCR was less or absent when cells were pretreated with UVC. These results suggest that detection of an involvement of hMLHl and hMSH2 in TCR is dependent on UVC (254 nm) fluence to cells. We have also used these two reporter gene assays to examine the role of hMSH2 and hMLHl in the repair of oxidative DNA damage induced by UV A light (335-400 nm) and H20 2• UV A and H20 2 produce a number of oxidative lesions in DNA (such as 8hydroxyguanines and thymine glycols) that are repaired by the base excision repair (BER) pathway. \ve show a reduced HCR for B-galactosidase expression of UVAtreated AdHCMVlccZ in hMSH2-deficient LoVo human colon adenocarcinoma cells compared to their hMSH2-proficient counterpart SW480 cells, but not in hMLHl-deficient HCT116 human colon adenocarcinoma cells compared to the hMLHl-proficient HCT116-chr3 cells. We also show that pre-treatment of cells with UVA enhances reporter gene expression to higher levels and at lower UV A fluences in Lo Vo compared to SW480 cells but not in HCT116 compared to HCT116-chr3 cells. These results suggest an involvement of hMSH2 but not hMLHl in the repair of UVA-induced oxidative DNA damage. In contrast, no detectable differences were observed between SW480 and LoVo cells, as well as HCT116-chr3 compared to HCT116 cells, in both of the reporter gene assays that used H20 2 as the DNA damaging agent. Based on these results, these findings suggest that neither hMSH2 nor hMLHl play a significant role in the repair of oxidative damage induced by H202. / Thesis / Master of Science (MS)