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Lawrence F. Povirk - One of the best experts on this subject based on the ideXlab platform.

  • Extreme cytotoxicity and susceptibility to hprt mutagenesis in Ku-deficient xrs-6 cells treated with bleomycin in Plateau Phase.
    Mutagenesis, 2005
    Co-Authors: Tong Zhou, Lawrence F. Povirk
    Abstract:

    In an attempt to determine the possible role of Ku-dependent end joining in mutagenesis resulting from DNA double-strand breaks, mutations induced by bleomycin at the hprt locus in Plateau Phase normal CHO-K1 and Ku-deficient xrs-6 cells were examined. Plateau Phase xrs-6 cells were 500-fold more sensitive to chronic bleomycin treatment than were CHO-K1 cells. XRCC4-deficient XR-1 cells were approximately 100-fold and DNA-PKcs-deficient XR-C1 and V-3 cells 15- to 30-fold more sensitive than CHO-K1 cells. These hypersensitivities are much greater than those previously reported for acute treatments with bleomycin or ionizing radiation. While the induced mutation frequencies at comparable levels of survival were slightly lower in xrs-6 cells, mutations were induced by bleomycin at much lower concentrations in xrs-6 than in CHO-K1 cells. For both cell lines bleomycin treatment resulted in a marked increase in the incidence of complete hprt deletions, while point mutations in hprt cDNA were rare. The results suggest that bleomycin-induced double-strand breaks tend to generate very large deletions in both cell lines and that this effect occurs at much lower levels of double-strand breaks in Ku-deficient than in normal cells.

  • Base substitutions, targeted single-base deletions, and chromosomal translocations induced by bleomycin in Plateau-Phase mammary epithelial cells.
    Radiation research, 2002
    Co-Authors: Kedar V. Inamdar, Kristi C. Turner, Colleen Jackson-cook, Lawrence F. Povirk
    Abstract:

    Abstract Yu, Y., Inamdar, K. V., Turner, K., Jackson-Cook, C. K. and Povirk, L. F. Base Substitutions, Targeted Single-Base Deletions, and Chromosomal Translocations Induced by Bleomycin in Plateau-Phase Mammary Epithelial Cells. Radiat. Res. 158, 327–338 (2002). Previous work showed that treatment of Plateau-Phase Chinese hamster ovary cells with the radiomimetic double-strand cleaving agent bleomycin induced very small deletions as well as interchromosomal reciprocal translocations, both of which could be ascribed to errors in end joining of DNA double-strand breaks. In an attempt to assess the possible role of TP53 in suppressing such repair errors, bleomycin-induced mutagenesis at the HPRT locus was examined in immortalized 184B5 human mammary epithelial cells (TP53+), and in a TP53-defective derivative, 184B5-E6tfxc6. For both cell lines, the most frequent bleomycin-induced mutations were base substitutions, with no apparent targeting to major bleomycin lesions. However, both lines also sustained sin...

  • enhanced amsacrine induced mutagenesis in Plateau Phase chinese hamster ovary cells with targeting of 1 frameshifts to free 3 ends of topoisomerase ii cleavable complexes
    Cancer Research, 1999
    Co-Authors: Kathleen Patteson, Peng Wang, Lawrence F. Povirk
    Abstract:

    Previous work showed that the DNA double-strand cleaving agents bleomycin and neocarzinostatin were more mutagenic in Plateau-Phase than in log-Phase cells. To determine whether topoisomerase II poisons that produce double-strand breaks by trapping of cleavable complexes would, likewise, induce mutations specific to Plateau-Phase cells, aprt mutations induced by amsacrine in both log-Phase and Plateau-Phase CHO cells were analyzed. The maximum aprt mutant frequencies obtained were 7 × 10-6 after treatment with 0.02 μm amsacrine in log Phase and 27 × 10-6 after treatment with 1 μm amsacrine in Plateau Phase, compared with a spontaneous frequency of <1 × 10-6. Base substitutions dominated the spectrum of mutations in log-Phase cells, but were much less prevalent in Plateau-Phase cells. Both spectra also included small deletions, insertions and duplications, as well as few large-scale deletions or rearrangements. About 5% of the log-Phase mutants and 16% of the Plateau-Phase mutants were +1 frameshifts, and all but one of these were targeted to potential free 3′ termini of cleavable complexes, as determined by mapping of cleavage sites in DNA treated with topoisomerase II plus amsacrine in vitro . Thus, these insertions may arise from templated extension of the exposed 3′ terminus by a DNA polymerase, followed by resealing of the strand, as shown previously for acridine-induced frameshifts in T4 phage.

  • Enhanced Amsacrine-induced Mutagenesis in Plateau-Phase Chinese Hamster Ovary Cells, with Targeting of +1 Frameshifts to Free 3′ Ends of Topoisomerase II Cleavable Complexes
    Cancer research, 1999
    Co-Authors: Kathleen Patteson, Peng Wang, Lawrence F. Povirk
    Abstract:

    Previous work showed that the DNA double-strand cleaving agents bleomycin and neocarzinostatin were more mutagenic in Plateau-Phase than in log-Phase cells. To determine whether topoisomerase II poisons that produce double-strand breaks by trapping of cleavable complexes would, likewise, induce mutations specific to Plateau-Phase cells, aprt mutations induced by amsacrine in both log-Phase and Plateau-Phase CHO cells were analyzed. The maximum aprt mutant frequencies obtained were 7 × 10-6 after treatment with 0.02 μm amsacrine in log Phase and 27 × 10-6 after treatment with 1 μm amsacrine in Plateau Phase, compared with a spontaneous frequency of

T. Kawabata - One of the best experts on this subject based on the ideXlab platform.

  • CI Aquilae: a recurrent nova with an unusually long Plateau Phase
    Monthly Notices of the Royal Astronomical Society, 2003
    Co-Authors: Katsura Matsumoto, Makoto Uemura, Taichi Kato, Ryoko Ishioka, T. Kawabata
    Abstract:

    We present the results of optical photometry of the recurrent nova CI Aql in a later Phase of the outburst which occurred in 2000. Our observation revealed that the object reached the quiescent level between 2001 December and 2002 April, and therefore that CI Aql is a unique recurrent nova characterized by an extremely long (1.4-1.7 yr) Plateau Phase. The light curve obtained in the outburst suggests that the object is the first example of an intermediate between classical and recurrent novae. In comparison with the estimation given in published theoretical calculations, the long duration of the Plateau Phase supports a higher hydrogen content of the white dwarf envelope, whereas such an abundance of hydrogen requires a later cessation of the wind, which is in disagreement with the sudden fading observed in late November of 2000. The light curve obtained in the later Phase of the outburst indicates that the object was fainter and the gradual decline was steeper than predicted. These discrepancies between the observation and the theoretical prediction demand a drastic modification of the present model of CI Aql.

  • ci aquilae a recurrent nova with an unusually long Plateau Phase
    arXiv: Astrophysics, 2002
    Co-Authors: Katsura Matsumoto, Makoto Uemura, Taichi Kato, Ryoko Ishioka, T. Kawabata
    Abstract:

    We present the results of optical photometry of the recurrent nova CI Aql in later Phase of the outburst which occurred in 2000. Our observation revealed that the object reached the quiescent level between 2001 December and 2002 April and therefore that CI Aql is a unique recurrent nova characterized by an extremely long (1.4--1.7 yr) Plateau Phase. The light curve obtained in the outburst suggests that the object is the first example of an intermediate between classical novae and recurrent novae. In comparison with estimation given in published theoretical calculations, the long duration of the Plateau Phase supports a higher hydrogen content of the white-dwarf envelope, while such an abundance of hydrogen requires a later cessation of the wind which is in disagreement with the sudden fading observed in late November of 2000. The light curve obtained in later Phase of the outburst indicates that the object was fainter and the gradual decline was steeper than predicted. These discrepancies between the observation and theoretical prediction require drastic modification of the present model of CI Aql.

Makoto Uemura - One of the best experts on this subject based on the ideXlab platform.

  • Discovery of a Short Plateau Phase in the Early Evolution of a Gamma-Ray Burst Afterglow
    Publications of the Astronomical Society of Japan, 2003
    Co-Authors: Makoto Uemura, Taichi Kato, Ryoko Ishioka, H Yamaoka
    Abstract:

    We report on optical observations during the first hour of the gamma-ray burst (GRB) afterglow of GRB 021004. Our observations revealed the existence of a short Plateau Phase, in which the afterglow remained at almost constant brightness, before an ordinary rapid-fading Phase. This Plateau Phase lasted for about 2 hours from 0.024 to 0.10d after the burst, which corresponds to a missing blank of the early afterglow light curve of GRB 990123. We propose that the Plateau Phase can be interpreted as being the natural evolution of synchrotron emission from the forward shock region of a blast wave. The time when the typical frequency of the synchrotron emission passes through the optical range has been predicted to be about 0.1 d after the burst, which is consistent with the observed light curve. Our scenario hence implies that the observed feature in GRB 021004 is a common nature of GRB afterglows.

  • CI Aquilae: a recurrent nova with an unusually long Plateau Phase
    Monthly Notices of the Royal Astronomical Society, 2003
    Co-Authors: Katsura Matsumoto, Makoto Uemura, Taichi Kato, Ryoko Ishioka, T. Kawabata
    Abstract:

    We present the results of optical photometry of the recurrent nova CI Aql in a later Phase of the outburst which occurred in 2000. Our observation revealed that the object reached the quiescent level between 2001 December and 2002 April, and therefore that CI Aql is a unique recurrent nova characterized by an extremely long (1.4-1.7 yr) Plateau Phase. The light curve obtained in the outburst suggests that the object is the first example of an intermediate between classical and recurrent novae. In comparison with the estimation given in published theoretical calculations, the long duration of the Plateau Phase supports a higher hydrogen content of the white dwarf envelope, whereas such an abundance of hydrogen requires a later cessation of the wind, which is in disagreement with the sudden fading observed in late November of 2000. The light curve obtained in the later Phase of the outburst indicates that the object was fainter and the gradual decline was steeper than predicted. These discrepancies between the observation and the theoretical prediction demand a drastic modification of the present model of CI Aql.

  • discovery of a short Plateau Phase in the early evolution of a gamma ray burst afterglow
    arXiv: Astrophysics, 2003
    Co-Authors: Makoto Uemura, Taichi Kato, Ryoko Ishioka, H Yamaoka
    Abstract:

    We report optical observations during the first hour of the gamma-ray burst (GRB) afterglow of GRB021004. Our observation revealed the existence of a short Plateau Phase, in which the afterglow remained at almost constant brightness, before an ordinary rapid fading Phase. This Plateau Phase lasted for about 2 hours from 0.024 to 0.10 d after the burst, which corresponds to a missing blank of the early afterglow light curve of GRB990123. We propose that the Plateau Phase can be interpreted as the natural evolution of synchrotron emission from the forward shock region of a blast wave. The time when the typical frequency of the synchrotron emission passes through the optical range has been predicted to be about 0.1 d after the burst, which is consistent with the observed light curve. Our scenario hence implies that the observed feature in GRB021004 is a common nature of GRB afterglows.

  • ci aquilae a recurrent nova with an unusually long Plateau Phase
    arXiv: Astrophysics, 2002
    Co-Authors: Katsura Matsumoto, Makoto Uemura, Taichi Kato, Ryoko Ishioka, T. Kawabata
    Abstract:

    We present the results of optical photometry of the recurrent nova CI Aql in later Phase of the outburst which occurred in 2000. Our observation revealed that the object reached the quiescent level between 2001 December and 2002 April and therefore that CI Aql is a unique recurrent nova characterized by an extremely long (1.4--1.7 yr) Plateau Phase. The light curve obtained in the outburst suggests that the object is the first example of an intermediate between classical novae and recurrent novae. In comparison with estimation given in published theoretical calculations, the long duration of the Plateau Phase supports a higher hydrogen content of the white-dwarf envelope, while such an abundance of hydrogen requires a later cessation of the wind which is in disagreement with the sudden fading observed in late November of 2000. The light curve obtained in later Phase of the outburst indicates that the object was fainter and the gradual decline was steeper than predicted. These discrepancies between the observation and theoretical prediction require drastic modification of the present model of CI Aql.

Taichi Kato - One of the best experts on this subject based on the ideXlab platform.

  • Discovery of a Short Plateau Phase in the Early Evolution of a Gamma-Ray Burst Afterglow
    Publications of the Astronomical Society of Japan, 2003
    Co-Authors: Makoto Uemura, Taichi Kato, Ryoko Ishioka, H Yamaoka
    Abstract:

    We report on optical observations during the first hour of the gamma-ray burst (GRB) afterglow of GRB 021004. Our observations revealed the existence of a short Plateau Phase, in which the afterglow remained at almost constant brightness, before an ordinary rapid-fading Phase. This Plateau Phase lasted for about 2 hours from 0.024 to 0.10d after the burst, which corresponds to a missing blank of the early afterglow light curve of GRB 990123. We propose that the Plateau Phase can be interpreted as being the natural evolution of synchrotron emission from the forward shock region of a blast wave. The time when the typical frequency of the synchrotron emission passes through the optical range has been predicted to be about 0.1 d after the burst, which is consistent with the observed light curve. Our scenario hence implies that the observed feature in GRB 021004 is a common nature of GRB afterglows.

  • CI Aquilae: a recurrent nova with an unusually long Plateau Phase
    Monthly Notices of the Royal Astronomical Society, 2003
    Co-Authors: Katsura Matsumoto, Makoto Uemura, Taichi Kato, Ryoko Ishioka, T. Kawabata
    Abstract:

    We present the results of optical photometry of the recurrent nova CI Aql in a later Phase of the outburst which occurred in 2000. Our observation revealed that the object reached the quiescent level between 2001 December and 2002 April, and therefore that CI Aql is a unique recurrent nova characterized by an extremely long (1.4-1.7 yr) Plateau Phase. The light curve obtained in the outburst suggests that the object is the first example of an intermediate between classical and recurrent novae. In comparison with the estimation given in published theoretical calculations, the long duration of the Plateau Phase supports a higher hydrogen content of the white dwarf envelope, whereas such an abundance of hydrogen requires a later cessation of the wind, which is in disagreement with the sudden fading observed in late November of 2000. The light curve obtained in the later Phase of the outburst indicates that the object was fainter and the gradual decline was steeper than predicted. These discrepancies between the observation and the theoretical prediction demand a drastic modification of the present model of CI Aql.

  • discovery of a short Plateau Phase in the early evolution of a gamma ray burst afterglow
    arXiv: Astrophysics, 2003
    Co-Authors: Makoto Uemura, Taichi Kato, Ryoko Ishioka, H Yamaoka
    Abstract:

    We report optical observations during the first hour of the gamma-ray burst (GRB) afterglow of GRB021004. Our observation revealed the existence of a short Plateau Phase, in which the afterglow remained at almost constant brightness, before an ordinary rapid fading Phase. This Plateau Phase lasted for about 2 hours from 0.024 to 0.10 d after the burst, which corresponds to a missing blank of the early afterglow light curve of GRB990123. We propose that the Plateau Phase can be interpreted as the natural evolution of synchrotron emission from the forward shock region of a blast wave. The time when the typical frequency of the synchrotron emission passes through the optical range has been predicted to be about 0.1 d after the burst, which is consistent with the observed light curve. Our scenario hence implies that the observed feature in GRB021004 is a common nature of GRB afterglows.

  • ci aquilae a recurrent nova with an unusually long Plateau Phase
    arXiv: Astrophysics, 2002
    Co-Authors: Katsura Matsumoto, Makoto Uemura, Taichi Kato, Ryoko Ishioka, T. Kawabata
    Abstract:

    We present the results of optical photometry of the recurrent nova CI Aql in later Phase of the outburst which occurred in 2000. Our observation revealed that the object reached the quiescent level between 2001 December and 2002 April and therefore that CI Aql is a unique recurrent nova characterized by an extremely long (1.4--1.7 yr) Plateau Phase. The light curve obtained in the outburst suggests that the object is the first example of an intermediate between classical novae and recurrent novae. In comparison with estimation given in published theoretical calculations, the long duration of the Plateau Phase supports a higher hydrogen content of the white-dwarf envelope, while such an abundance of hydrogen requires a later cessation of the wind which is in disagreement with the sudden fading observed in late November of 2000. The light curve obtained in later Phase of the outburst indicates that the object was fainter and the gradual decline was steeper than predicted. These discrepancies between the observation and theoretical prediction require drastic modification of the present model of CI Aql.

Ryoko Ishioka - One of the best experts on this subject based on the ideXlab platform.

  • Discovery of a Short Plateau Phase in the Early Evolution of a Gamma-Ray Burst Afterglow
    Publications of the Astronomical Society of Japan, 2003
    Co-Authors: Makoto Uemura, Taichi Kato, Ryoko Ishioka, H Yamaoka
    Abstract:

    We report on optical observations during the first hour of the gamma-ray burst (GRB) afterglow of GRB 021004. Our observations revealed the existence of a short Plateau Phase, in which the afterglow remained at almost constant brightness, before an ordinary rapid-fading Phase. This Plateau Phase lasted for about 2 hours from 0.024 to 0.10d after the burst, which corresponds to a missing blank of the early afterglow light curve of GRB 990123. We propose that the Plateau Phase can be interpreted as being the natural evolution of synchrotron emission from the forward shock region of a blast wave. The time when the typical frequency of the synchrotron emission passes through the optical range has been predicted to be about 0.1 d after the burst, which is consistent with the observed light curve. Our scenario hence implies that the observed feature in GRB 021004 is a common nature of GRB afterglows.

  • CI Aquilae: a recurrent nova with an unusually long Plateau Phase
    Monthly Notices of the Royal Astronomical Society, 2003
    Co-Authors: Katsura Matsumoto, Makoto Uemura, Taichi Kato, Ryoko Ishioka, T. Kawabata
    Abstract:

    We present the results of optical photometry of the recurrent nova CI Aql in a later Phase of the outburst which occurred in 2000. Our observation revealed that the object reached the quiescent level between 2001 December and 2002 April, and therefore that CI Aql is a unique recurrent nova characterized by an extremely long (1.4-1.7 yr) Plateau Phase. The light curve obtained in the outburst suggests that the object is the first example of an intermediate between classical and recurrent novae. In comparison with the estimation given in published theoretical calculations, the long duration of the Plateau Phase supports a higher hydrogen content of the white dwarf envelope, whereas such an abundance of hydrogen requires a later cessation of the wind, which is in disagreement with the sudden fading observed in late November of 2000. The light curve obtained in the later Phase of the outburst indicates that the object was fainter and the gradual decline was steeper than predicted. These discrepancies between the observation and the theoretical prediction demand a drastic modification of the present model of CI Aql.

  • discovery of a short Plateau Phase in the early evolution of a gamma ray burst afterglow
    arXiv: Astrophysics, 2003
    Co-Authors: Makoto Uemura, Taichi Kato, Ryoko Ishioka, H Yamaoka
    Abstract:

    We report optical observations during the first hour of the gamma-ray burst (GRB) afterglow of GRB021004. Our observation revealed the existence of a short Plateau Phase, in which the afterglow remained at almost constant brightness, before an ordinary rapid fading Phase. This Plateau Phase lasted for about 2 hours from 0.024 to 0.10 d after the burst, which corresponds to a missing blank of the early afterglow light curve of GRB990123. We propose that the Plateau Phase can be interpreted as the natural evolution of synchrotron emission from the forward shock region of a blast wave. The time when the typical frequency of the synchrotron emission passes through the optical range has been predicted to be about 0.1 d after the burst, which is consistent with the observed light curve. Our scenario hence implies that the observed feature in GRB021004 is a common nature of GRB afterglows.

  • ci aquilae a recurrent nova with an unusually long Plateau Phase
    arXiv: Astrophysics, 2002
    Co-Authors: Katsura Matsumoto, Makoto Uemura, Taichi Kato, Ryoko Ishioka, T. Kawabata
    Abstract:

    We present the results of optical photometry of the recurrent nova CI Aql in later Phase of the outburst which occurred in 2000. Our observation revealed that the object reached the quiescent level between 2001 December and 2002 April and therefore that CI Aql is a unique recurrent nova characterized by an extremely long (1.4--1.7 yr) Plateau Phase. The light curve obtained in the outburst suggests that the object is the first example of an intermediate between classical novae and recurrent novae. In comparison with estimation given in published theoretical calculations, the long duration of the Plateau Phase supports a higher hydrogen content of the white-dwarf envelope, while such an abundance of hydrogen requires a later cessation of the wind which is in disagreement with the sudden fading observed in late November of 2000. The light curve obtained in later Phase of the outburst indicates that the object was fainter and the gradual decline was steeper than predicted. These discrepancies between the observation and theoretical prediction require drastic modification of the present model of CI Aql.