• Proceedings of the Zoological Society Korea Conference
• /
• 1998.10b
• /
• pp.113-113
• /
• 1998

In Saccharomyces cerevisiae UV irradiation and a variety of chemical DNA -damaging agents induce the transcription of specific genes, including several involved in DNA repair. One of the best characterized of DNA -damage inducible genes is PHRI, which encodes the apoenzyme for DNA photolyase. Basal-level and damage-induced expression of PHRI require an upstream activation sequence, UASPHRI. Here we report the identification of the UlvIE6 gene of S. cerevisiae as a regulator of UASPHRl activity. Surprisingly, the effect of deletion of UME6 is growth phase dependent. In wild-type cells PHRI is induced in late exponential phase, concomitant with the initiation of glycogen accumulation that precedes the diauxic shift. Deletion of UNIE6 abolishes this induction, decreases the steady-state concentration of photolyase molecules and PHRI mRNA, and increases the UV sensitivity of a rad2 mutant. The results suggest that UM E6 contributes to the regulated expression of a subset of damage-responsive genes in yeast. Furthermore, the upstream repression sequence, URSPHRI, is required for repression and damage-induced expression of PHRl. Here we show identification of YER169W and YDR096W as putative regulators acting through $URS_{PHRI}$. These open reading frames were designated as RPHI (YERl69W) and RPH2 (YDR096W) indicating regulator of PHRI. Simultaneous disruption of both genes showed a synergistic effect, producing a four-fold increase in basal level expression and a similar decrease m the induction ratio following treatment of methyl methanesulfonate(MMS). Mutation of the sequence ($AG_4$) bound by Rphlp rendered the promoter of PHRI insensitive to changes in RPHI or RPH2 status. The data suggest that RPHI and RPH2 act as damage-responsive negative regulators of PHRI. Surprisingly, the sequence bound by Rphlp in vitro is found to be $AG_4$ which is identical to the consensus binding site for the regulators Msn2p and Msn4p involved in stress-induced expression. Deletion of MSN2 and MSN4 has little effect on the induction$.$ ratio following DNA damage. However, all deletions led to a significant decrease in basal-level and induced expression of PHRI. These results imply that MSN2 and MSN4 are positive regulators of P HRI but are not required for DNA damage repression. [Supported by grant from NIH]om NIH]

• Radiation Oncology Journal
• /
• v.11 no.2
• /
• pp.193-203
• /
• 1993

In understanding radiosensitivity a new concept of inherent radiosensitivity based on individuality and heterogeneity within a population has recently been explored. There has been some discussion of possible mechanism underlying differences in radiosensitivity between cells. Ataxia telangiectasia (AT), a rare autosomal recessive genetic disorder, is characterized by hypersensitivity to ionizing radiation and other DNA damaging agents at the cellular level. There have been a lot of efforts to describe the cause of this hypersensitivity to radiation. At the cellular level, chromosome repair kinetics study would be an appropriate approach. The purpose of this study was to better understand radiosensitivity En an approach to investigate kinetics of induction and repair of $G_2$ chromatic bleaks using normal, AT heterozygous (ATH), and AT homozygous lymphoblastoid cell lines. In an attempt to estimate initial damage, $9-{\beta}-D-arabinosyl-2-fluoroadenine,$ an inhibitor of DNA synthesis and repair, was used in this study. It was found from this study that radiation induces higher chromatid breaks in AT than in normal and ATH cells. There was no significant differences of initial chromatid breaks between normal and ATH cells. Repair kinetics was the same for all. So the higher level of breaks in AT $G_2$ cells is thought to be a reflection of the increased initial damage. The amount of initial damage correlated well with survival fraction at 2 Gy of cell survival curve following radiation. Therefore, the difference of radiosensitivity in terms of $G_2$ chromosomal sensitivity is thought to result from the difference of initial damage.

• Journal of Microbiology and Biotechnology
• /
• v.20 no.12
• /
• pp.1637-1646
• /
• 2010

The bacterium Deinococcus radiodurans is one of the most resistant organisms to ionizing radiation and other DNA-damaging agents. Although, at present, 30 Deinococcus species have been identified, the whole-genome sequences of most species remain unknown, with the exception of D. radiodurans (DRD), D. geothermalis, and D. deserti. In this study, comparative genomic hybridization (CGH) microarray analysis of three Deinococcus species, D. radiopugnans (DRP), D. proteolyticus (DPL), and D. radiophilus (DRPH), was performed using oligonucleotide arrays based on DRD. Approximately 28%, 14%, and 15% of 3,128 open reading frames (ORFs) of DRD were absent in the genomes of DRP, DPL, and DRPH, respectively. In addition, 162 DRD ORFs were absent in all three species. The absence of 17 randomly selected ORFs was confirmed by a Southern blot. Functional classification showed that the absent genes spanned a variety of functional categories: some genes involved in amino acid biosynthesis, cell envelope, cellular processes, central intermediary metabolism, and DNA metabolism were not present in any of the three deinococcal species tested. Finally, comparative genomic data showed that 120 genes were Deinococcus-specific, not the 230 reported previously. Specifically, ddrD, ddrO, and ddrH genes, previously identified as Deinococcus-specific, were not present in DRP, DPL, or DRPH, suggesting that only a portion of ddr genes are shared by all members of the genus Deinococcus.

• Journal of Life Science
• /
• v.19 no.4
• /
• pp.436-441
• /
• 2009

B23/nucleophosmin, a nucleolar protein, translocates into the nucleus from the nucleolus when cells are damaged by extracellular stresses. Recently, it was shown that such translocation of B23/nucleophosmin in normal fibroblasts under stress conditions increases both the stability and activation of the p53 protein by disrupting its interaction with MDM2. Senescent cells have a single large nucleolus and a diminished capacity to induce p53 stability upon exposure to various DNA damaging agents. To investigate the role of B23/nucleophosmin in p53 stability in senescent cells, we established a senescence model system by expressing the ras oncogene in IMR90 cells. The stability of p53 was reduced in these cells in response to nucleolar stress, although the level of B23/nucleophosmin protein was not changed. In addition, p53 did not accumulate in the nucleus and B23/nucleophosmin did not translocate into the nucleoplasm. The binding affinity of B23/nucleophosmin with p53 was reduced in senescent cells, whereas the interaction between MDM2 and p53 was stable. Taken together, the stability of p53 in ras-induced senescent cells may be influenced by the ability of B23/nucleophosmin to interact with p53 in response to nucleolar stress.

• Radiation Oncology Journal
• /
• v.21 no.3
• /
• pp.227-237
• /
• 2003

Purpose: The human chronic myelogenous leukemia cell line, K562, expresses the chimeric bcr-abl oncoprotein, whose deregulated protein tyrosine kinase activity antagonizes via DNA damaging agents. Previous experiments have shown that nanomolar concentrations of herbimycin A (HWA) coupled with X-irradiation have a synergistic effect in inducing apoptosis in the Ph-positive K562 leukemia cell line, but genistein, a PTK inhibitor, is non selective for the radiation-induced apoptosils on $p210^{bcr/abl}$ protected K562 cells. In these experiments, the cytoplasmic signal transduction pathways, the Induction on a number of transcription factors and the differential gene expression in this model were investigated. Materials and Methids: K562 cells in the exponential growth phase were used in this study. The cells were irradiated with 0.5-12 Gy, using a 6 Mev Linac (Clinac 1800, Varian, USA). Immediately after irradiation, the cells were treated with $0.25/muM$ of HMA and $25/muM$ of genistein, and the expressions and the activities of abl kinase, MAPK family, NF- kB, c-fos, c-myc, and thymidine kinase1 (TK1) were examined. The differential gene expressions induced by PTK inhibitors were also investigated. Results: The modulating effects of herbimycin A and genistein on the radiosensitivity of K562 cells were not related to the bcr-abl kinase activity. The signaling responses through the MAPK family of proteins, were not involved either in association with the radiation-induced apoptosis, which is accelerated by HMA, the expression of c-myc was increased. The combined treatment of genistein, with irradiation, enhanced NF- kB activity and the TK1 expression and activity. Conclusion: The effects of HMA and genistein on the radiosensitivity on the K562 cells were not related to the bcr-abl kinase activity in this study, another signaling pathway, besides the WAPK family responses to radiation to K562 cells, was found. Further evaluation using this model will provide valuable information for the optional radiosensitization or radioprotection.