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G F Strniste

Publications and source records attributed to G F Strniste.

At least 19 recordsLinked to original sources
PubMed1997

Heritable genetic alterations in a xeroderma pigmentosum group G/Cockayne syndrome pedigree.

A search for genetic alterations within the XPG gene has been conducted on skin and blood cells cultured from a newly characterized xeroderma pigmentosum (XP) patient (XP20BE). This patient is the ninth known case that falls into the extremely rare XP complementation group G. Four genetic markers within the XPG gene (including two polymorphisms) demonstrated the Mendelian distribution of this gene from the parents to the patient and to an unaffected sibling. The patient (XP20BE) inherited a G to T transversion from his father in exon 1 of the XPG gene that resulted in the conversion of a glutamic acid at codon 11 to a termination codon. The patient also inherited an XP-G allele from his mother that produces an unstable or poorly expressed message. The cause of the latter defect is still uncertain. In addition to these alterations, XP20BE cDNA contained an mRNA species with a large splicing defect that encompassed a deletion from exon 1 to exon 14. This splicing defect, however, appears to be a naturally occurring low-frequency event that results from abnormal splicing that occurs between certain conserved non-consensus splicing signals within the human XPG gene.

Cells, Cultured↗
PubMed1996

Ultraviolet-induced movement of the human DNA repair protein, Xeroderma pigmentosum type G, in the nucleus.

Xeroderma pigmentosum type G (XPG) is a human genetic disease exhibiting extreme sensitivity to sunlight. XPG patients are defective XPG endonuclease, which is an enzyme essential for DNA repair of the major kinds of solar ultraviolet (UV)-induced DNA damages. Here we describe a novel dynamics of this protein within the cell nucleus after UV irradiation of human cells. Using confocal microscopy, we have localized the immunofluorescent, antigenic signal of XPG protein to foci throughout the cell nucleus. Our biochemical studies also established that XPG protein forms a tight association with nuclear structure(s). In human skin fibroblast cells, the number of XPG foci decreased within 2 h after UV irradiation, whereas total nuclear XPG fluorescence intensity remained constant, suggesting redistribution of XPG from a limited number of nuclear foci to the nucleus overall. Within 8 h after UV, most XPG antigenic signal was found as foci. Using beta-galactosidase-XPG fusion constructs (beta-gal-XPG) transfected into HeLa cells, we have identified a single region of XPG that is evidently responsible both for foci formation and for the UV dynamic response. The fusion protein carrying the C terminus of XPG (amino acids 1146-1185) localized beta-gal specific antigenic signal to foci and to the nucleolus regions. After UV irradiation, antigenic beta-gal translocated reversibly from the subnuclear structures to the whole nucleus with kinetics very similar to the movements of XPG protein. These findings lead us to propose a model in which distribution of XPG protein may regulate the rate of DNA repair within transcriptionally active and inactive compartments of the cell nucleus.

Amino Acid Sequence↗
PubMed1996

Multiple nuclear localization signals in XPG nuclease.

We report here evidence for the mechanism of nuclear localization of XPG nuclease in human cells. Several candidate nuclear localization signal (NLS) peptides have been proposed for XPG protein. We have identified XPG peptides containing functional NLS and a potential nuclear retention signal (NRS) using in situ immunofluorescene localization of transiently expressed beta-galactosidase fusion proteins. Two XPG regions with putative NLS [amino acid (AA) coordinates: NLS-B (AA 1057-1074) and NLS-C (AA 1171-1185)] were each shown to independently localize the beta-gal extensively (> 80%) to the nucleus of HeLa cells. The C-terminus peptide containing NLS-C, an NLS conserved evolutionarily between yeasts and humans, also directed sub-localization of beta-galactosidase to intranuclear foci reminiscent of native XPG protein, as well as to peri-nucleolar regions. Peptides in the putative XPG 'NLS domain' (AA approximately 1051-1185) apparently function in concert for nuclear localization and also for retention of XPG in nuclear matrix-associated foci. Evidence presented elsewhere (Park et al., 1995) indicates that the peptide containing NLS-C (AA 1146-1185) also regulates the dynamic localization of XPG in the nucleus following UV-irradiation.

Amino Acid Sequence↗
PubMed1995

XPG protein has a structure-specific endonuclease activity.

Biochemically active human DNA repair protein, xeroderma pigmentosum G (XPG), was overexpressed in insect cells by a recombinant baculovirus. The recombinant baculovirus produced XPG with a mobility of approximately 185 kDa in a denaturing polyacrylamide gel. Indirect immunofluorescence studies demonstrated that the recombinant full-length XPG protein was expressed predominantly as a nuclear protein. The recombinant XPG protein was purified to apparent homogeneity using Q-sepharose, S-300 size exclusion, and Mono Q column chromatography. XPG protein showed a structure-specific DNA endonuclease activity, and a preferential affinity to single-stranded DNA and RNA compared to double-stranded DNA.

Animals↗
PubMed1995

Interspecific complementation between mouse and Chinese hamster cell mutants hypersensitive to ionizing radiation.

Interspecific and intraspecific hybrids were formed between mouse and Chinese hamster cell mutants hypersensitive to ionizing radiation and their radiosensitivities were examined. Chinese hamster cell mutants irs1, irs2 and irs3 and mouse mammary carcinoma cell mutants SX9 and SX10 have been found to belong to five different complementation groups. A radiosensitive mouse lymphoma cell line L5178Y-S has been demonstrated to be different from the X-ray sensitive mouse cell mutants M10 and LX830, both of which are derived from L5178Y cells, in their complementation groups. L5178Y-S is also distinct from SX9 and SX10.

Animals↗
PubMed1993

Human ERCC5 cDNA-cosmid complementation for excision repair and bipartite amino acid domains conserved with RAD proteins of Saccharomyces cerevisiae and Schizosaccharomyces pombe.

Several human genes related to DNA excision repair (ER) have been isolated via ER cross-species complementation (ERCC) of UV-sensitive CHO cells. We have now isolated and characterized cDNAs for the human ERCC5 gene that complement CHO UV135 cells. The ERCC5 mRNA size is about 4.6 kb. Our available cDNA clones are partial length, and no single clone was active for UV135 complementation. When cDNAs were mixed pairwise with a cosmid clone containing an overlapping 5'-end segment of the ERCC5 gene, DNA transfer produced UV-resistant colonies with 60 to 95% correction of UV resistance relative to either a genomic ERCC5 DNA transformant or the CHO AA8 progenitor cells. cDNA-cosmid transformants regained intermediate levels (20 to 45%) of ER-dependent reactivation of a UV-damaged pSVCATgpt reporter plasmid. Our evidence strongly implicates an in situ recombination mechanism in cDNA-cosmid complementation for ER. The complete deduced amino acid sequence of ERCC5 was reconstructed from several cDNA clones encoding a predicted protein of 1,186 amino acids. The ERCC5 protein has extensive sequence similarities, in bipartite domains A and B, to products of RAD repair genes of two yeasts, Saccharomyces cerevisiae RAD2 and Schizosaccharomyces pombe rad13. Sequence, structural, and functional data taken together indicate that ERCC5 and its relatives are probable functional homologs. A second locus represented by S. cerevisiae YKL510 and S. pombe rad2 genes is structurally distinct from the ERCC5 locus but retains vestigial A and B domain similarities. Our analyses suggest that ERCC5 is a nuclear-localized protein with one or more highly conserved helix-loop-helix segments within domains A and B.

Amino Acid Sequence↗
PubMed1993

A shuttle vector system for studying ionizing radiation-induced mutagenesis in mammalian cells.

A shuttle vector system was developed to quantitate and analyze ionizing radiation-induced mutation in mammalian host cells, COS-1 and CV-1. The shuttle vector pSV2-lacY, which was constructed to detect both point mutations and deletions, was irradiated in vitro with 60Co gamma rays before introduction into unirradiated host cells. The plasmid was then isolated and reintroduced into HB101 (lacY-) bacterial host cells for identification of mutated lacY marker genes. Gamma-irradiation produced a decrease of the survival (recovery) and an increase of mutation of the shuttle vector. The mutated shuttle vector molecules were examined for structural changes by means of restriction endonuclease digestion and agarose gel electrophoresis. A dose dependent increase was observed in the percentages of gross alteration events of total mutations in mammalian host. This system will be useful for studies of ionizing radiation-induced mutagenesis.

Animals↗
PubMed1992

Effect of dose rate on the survival of irradiated human skin fibroblasts.

The survival of cells in density-inhibited, confluent cultures maintained at 37 degrees C was examined following exposure to 137Cs gamma rays at low dose rates (0.023 or 0.153 Gy/h) or to 60Co gamma rays at a single high dose rate (0.70-0.75 Gy/min). Cells from an ataxia telangiectasia (AT) homozygote showed no dose-rate effect, whereas a three- to fivefold increase in D0 was observed for all other cell strains exposed at low dose rates. The magnitude of the dose-rate effect did not differ significantly among cells from persons with hereditary retinoblastoma, basal cell nevus syndrome, or AT-heterozygote compared with normal cell strains, and was not related to the size of the shoulder (extrapolation number) of the survival curve. Furthermore, no differences in the capacity for the repair of potentially lethal damage during confluent holding were observed among these latter cell strains.

Ataxia Telangiectasia↗
PubMed1991

Response of X-ray-sensitive CHO mutant cells (xrs-6c) to radiation. II. Relationship between cell survival and the induction of chromosomal damage with low doses of alpha particles.

The induction of cytotoxicity, chromosomal aberrations, and sister chromatid exchanges (SCEs) was measured in CHO K-1c cells and in isogenic X-ray-sensitive mutant xrs-6c cells that had been irradiated with X rays and alpha particles in isoleucine-deficient alpha-minimal essential medium in G1 phase of the cell cycle. There was a noticeable shoulder region on the survival curve for CHO K-1c cells irradiated with very low doses of alpha particles, whereas this feature was absent for xrs-6c cells with alpha-particle doses as low as 0.5 cGy. Higher frequencies of chromatid-type aberrations were induced in G1-phase xrs-6c cells than in G1-phase CHO K-1c cells by both gamma- and alpha-particle irradiation. Induction of nonlethal chromosomal aberrations was observed following exposure to 2-6 cGy of alpha particles, doses yielding 97-100% cell survival. Irradiation with 0.5 cGy of alpha particles induced SCE; nearly 60% of irradiated cells contained significantly increased levels of SCE. However, only 3% of the nuclei of cells exposed to 0.5 cGy of alpha-particle radiation were actually traversed by an alpha particle. The observation that a large fraction of cells apparently survive exposure to very low doses of alpha-particle radiation with persistent genetic damage manifested by both chromosomal aberrations and SCEs may have important implications for the carcinogenic hazards of high-LET radiation.

Alpha Particles↗
PubMed1990

Cytogenetic effects of extremely low doses of plutonium-238 alpha-particle irradiation in CHO K-1 cells.

CHO K-1 cells were irradiated during the G1 phase with 0.5-6 rad of alpha particles. There was no appreciable cell killing in this low dose range. Significantly increased frequencies of sister-chromatid exchanges were induced by doses as low as 0.5 rad of alpha-particle irradiation, whereas increased numbers of chromosomal aberrations were observed following exposure to 2 rad. These results suggest that very low doses of alpha radiation may lead to radiation-induced genetic alterations.

Alpha Particles↗
PubMed1989

Response of X-ray-sensitive CHO mutant cells to gamma radiation. I. Effects of low dose rates and the process of repair of potentially lethal damage in G1 phase.

X-ray-sensitive CHO mutants (xrs-5 and xrs-6) were exposed to isoleucine-deficient (IL-) medium for 24-36 h to accumulate G1-phase cells. Cells exposed to IL- medium for up to 5 days did not show significant changes in plating efficiency when returned to normal medium. Nearly confluent cultures of IL- -treated cells were irradiated with either 60Co gamma rays (75 cGy/min) or 137Cs gamma rays (2.7, 6.0, or 15.3 cGy/h). A significant reduction (approximately 2.5-fold) in the radiation sensitivity of the parental CHO K-1 cells was observed for chronic low-dose-rate radiation exposure compared to the results obtained for acute high-dose-rate exposure. However, no noticeable differences were observed in the survival curves of either xrs-5 or xrs-6 cells when low-dose-rate and acute exposures were compared. CHO K-1 cells exhibited potentially lethal damage repair while held in IL- medium after gamma irradiation, whereas no repair was observed in either of the radiation-sensitive mutant lines examined at similar survival levels.

Animals↗
PubMed1986

1-Nitropyrene: a mutagenic product induced by the action of near ultraviolet light on 1-aminopyrene.

A solution of 1-aminopyrene in dimethyl sulfoxide exposed to an artificial source of near ultraviolet light (600 kJ/m2) induced significant direct-acting mutagenicity in the Ames/Salmonella plating assay utilizing strain TA98. High-performance liquid chromatography of this solution resulted in a fraction that was mutagenic on TA98 but inactive on a nitroreductase-deficient strain of Salmonella (TA98NR). This observation suggested the presence of a nitro-containing compound. Mass spectral analysis confirmed that 1-nitropyrene was the active photoproduct in this fraction. These data implicate photochemical transformation of primary aromatic amines as an alternative mechanism by which nitroaromatic compounds can be formed in the environment.

Chromatography, High Pressure Liquid↗
PubMed1986

2-Nitrofluoren-9-one: a unique mutagen formed in the photo-oxidation of 2-aminofluorene.

Exposure of solutions of 2-aminofluorene (2-AF, dissolved in dimethylsulfoxide) to near ultraviolet light (u.v.a. wavelengths of 320-400 nm) results in the formation of a variety of photo-products, several of which are direct-acting mutagens in the Ames/Salmonella standard-plate assay. Previously published results from our laboratory have described the chemical identification and kinetics of formation of two of these photo-induced mutagens, 2-nitrosofluorene and 2-nitrofluorene. In this report we present recent data concerning the isolation and chemical identification of another mutagenic photoproduct of u.v.a.-irradiated 2-AF, 2-nitrofluoren-9-one (2-NO2F-9-one). Data are also presented concerning the kinetics of phototransformation of 2-aminofluoren-9-one, an early-appearing and predominant photoproduct in u.v.a.-irradiated solutions of 2-AF, into 2-NO2F-9-one. It is well established that N-oxidation is a critical step in the biotransformations (i.e. enzymatic metabolism) of primary aromatic amines into proximate mutagens/carcinogens. In addition to u.v.a.-mediated N-oxidation of aromatic amines, selective ring photo-oxidation can also occur, resulting in, for example, the production of a carbonyl group at the 9-position of the fluorene molecule. The formation of mutagenic 2-NO2F-9-one in the photochemical oxidation of 2-AF appears to be unique to this process.

Chromatography, High Pressure Liquid↗
PubMed1985

Photochemical oxidation of 2-aminofluorene: correlation between the induction of direct-acting mutagenicity and the formation of nitro and nitroso aromatics.

The kinetics of near ultraviolet light-mediated phototransformation of 2-aminofluorene (2-AF) was studied using high performance liquid chromatography (HPLC) and the Ames/Salmonella mutagenicity bioassay. Employing tester strains TA98, TA1538, and the nitroreductase-deficient TA98NR without the addition of exogenous metabolic enzymes, we were able to detect and discriminate between the UVA exposure-dependent formation of two stable photoproducts, 2-nitrosofluorene (2-NOF) and 2-nitrofluorene (2-NO2F). Mutagenicity of irradiated 2-AF solutions (using dimethyl sulfoxide as a solvent) in the various tester strains indicates the rapid formation of the photo-labile 2-NOF, after which 2-NO2F accounts for the preponderance of mutagenic activity. Continued UVA irradiation (greater than 72 h at 6.8 J/m2/s) of 2-AF results in the formation of greater than 30 photoproducts resolvable on HPLC, several of which, in addition to 2-NOF and 2-NO2F, are mutagenic on Salmonella but are chemically undefined to date. Prolonged irradiation ultimately destroys the photo-induced mutagenicity of 2-AF. However, UVA-induced 2-AF photoproducts are stable for several weeks when stored in sealed vials in the dark. Light potentiated oxidation of aromatic amines constitutes an alternative mechanism for the transformation of aromatic amines into proximate mutagens/carcinogens.

Dose-Response Relationship, Radiation↗
PubMed1984

Phototransformation of 2-aminofluorene into N-oxidized mutagens.

Exposure to sunlight or artificial sources of near u.v. light transforms 2-aminofluorene into a direct-acting mutagenic agent in the Ames/Salmonella histidine reversion bioassay. H.p.l.c. fractionation indicates that the majority of this mutagenic activity elutes as a single A254 absorbance peak. I.r. spectroscopy of the fractionated active fraction shows the presence of significant quantities of 2-nitrofluorene. The use of a nitroreductase deficient strain of Salmonella, coupled with t.l.c. analysis, however, also indicates the presence of a minor component whose mutagenic and t.l.c. properties are identical with 2-nitrosofluorene. These results implicate a specific mechanism by which aromatic amines can be photo-oxidized to potentially harmful genotoxic agents.

Fluorenes↗
PubMed1984

DNA-mediated cotransfer of excision repair capacity and drug resistance into chinese hamster ovary mutant cell line UV-135.

We have investigated DNA-mediated transfer of aminopterin resistance conferred by plasmid and UV resistance conferred by genomic DNA to the Chinese hamster ovary (CHO) cell line UV-135, a UV-sensitive mutant defective in nucleotide excision repair. Plasmid pSV2gpt-CaPO4 coprecipitates induced aminopterin resistance with equal efficiency in the 6-thioguanine-resistant, aminopterin-sensitive, repair-proficient parental line AA8-4(tg-1) and in UV-135(tg-2). Genetic and molecular evidence for genomic DNA-mediated transformation of UV-135(tg-2) cells with a putative excision repair gene were obtained by demonstrating that: (i) UV resistance transformation is dependent upon and specific for genomic DNA from excision repair-competent CHO cells: (ii) UV and drug coresistant colonies are bona fide transferants as verified by hybridization and Southern blotting analysis of pSV2gpt sequences in their genomic DNAs: (iii) confirmed transferants exhibit partial to near normal UV resistances for colony formation: and (iv) UVr transferants have near normal levels of excision repair capacity. The overall frequency of drug and UV resistance cotransformation was 8 X 10(8) per cell plated. This frequency was ca. 200- to 500-fold greater than that expected from coincident but independent UVr reversion and plasmid gene transfer events. DNA transfer techniques with this CHO system will be useful for further analysis of the essential structural DNA sequences, gene cloning, and expression of functional excision repair genes.

Aminopterin↗
PubMed1984

The genotoxicity of alpha particles in human embryonic skin fibroblasts.

Cell inactivation and induced mutation frequencies at the hypoxanthine-guanine phosphoribosyl transferase (HGPRT) locus have been measured in cultured human fibroblasts (GM10) exposed to alpha particles from 238Pu (LET at the cell surface was 100 keV/microns) and 250 kVp X rays. The survival curves resulting from exposure to alpha particles are exponential. The mean lethal dose, D0, is approximately 1.3 Gy for X rays and 0.25 Gy for alpha particles. As a function of radiation dose, mutation induction at the HGPRT locus was linear for alpha particles whereas the X-ray-induced mutation data were better fitted by a quadratic function. When mutation frequencies were plotted against the log of survival, mutation frequency at a given survival level was greater in cells exposed to alpha particles than to X rays.

Alpha Particles↗