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A Ronen

Publications and source records attributed to A Ronen.

At least 19 recordsLinked to original sources
PubMed2004

Flint mining in prehistory recorded by in situ-produced cosmogenic 10Be.

The development of mining to acquire the best raw materials for producing stone tools represents a breakthrough in human technological and intellectual development. We present a new approach to studying the history of flint mining, using in situ-produced cosmogenic 10Be concentrations. We show that the raw material used to manufacture flint artifacts approximately 300,000 years old from Qesem Cave (Israel) was most likely surface-collected or obtained from shallow quarries, whereas artifacts of the same period from Tabun Cave (Israel) were made of flint originating from layers 2 or more meters deep, possibly mined or quarried by humans.

Journal Article↗
PubMed2001

Human DNA repair genes.

DNA repair systems are essential for the maintenance of genome integrity. Consequently, the disregulation of repair genes can be expected to be associated with significant, detrimental health effects, which can include an increased prevalence of birth defects, an enhancement of cancer risk, and an accelerated rate of aging. Although original insights into DNA repair and the genes responsible were largely derived from studies in bacteria and yeast, well over 125 genes directly involved in DNA repair have now been identified in humans, and their cDNA sequence established. These genes function in a diverse set of pathways that involve the recognition and removal of DNA lesions, tolerance to DNA damage, and protection from errors of incorporation made during DNA replication or DNA repair. Additional genes indirectly affect DNA repair, by regulating the cell cycle, ostensibly to provide an opportunity for repair or to direct the cell to apoptosis. For about 70 of the DNA repair genes listed in Table I, both the genomic DNA sequence and the cDNA sequence and chromosomal location have been elucidated. In 45 cases single-nucleotide polymorphisms have been identified and, in some cases, genetic variants have been associated with specific disorders. With the accelerating rate of gene discovery, the number of identified DNA repair genes and sequence variants is quickly rising. This report tabulates the current status of what is known about these genes. The report is limited to genes whose function is directly related to DNA repair.

Chromosomes, Human↗
PubMed1997

Variable aberrant cDNAs in single diphtheria toxin-resistant human fibroblasts.

We treated transformed human fibroblasts with diphtheria toxin (DT) and isolated 40 single cells that were toxin resistant but unable to propagate. In 13 of them toxin resistance was associated with the presence of one or more aberrant transcripts of the structural gene for elongation factor 2 (EF-2). cDNA obtained from these transcripts had 164-447 bp-long deletions. Each of these deletions was associated with 2-8 base pairs-long repeats at its breakpoints. Only 10 out of 16 cDNA deletions were associated with presumed exon junctions. A role is suggested for errors in transcription in producing the aberrant transcripts which gave rise to the deletion-bearing cDNA species.

Cell Division↗
PubMed1991

[We disown death].

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Attitude of Health Personnel↗
PubMed1991

Dominant lethal cell mutants detected by the autoradiographic assay for exotoxin A resistance.

The autoradiographic assay (AR assay) for P. aeruginosa exotoxin A (PE) resistance in cultured mouse fibroblasts detects mutants able to synthesize proteins in the presence of the toxin, presumably due to mutations in the structural gene for elongation factor 2 (EF-2). Detection by the AR assay of PER cells is independent of their ability to divide. The frequencies of both spontaneous and mutagen-induced PER cells are higher than those detected by the conventional colony assay. Examination of phenotypic expression times in the PER cells, and of their in situ proliferation, reveals that this higher sensitivity of the AR assay is due to its ability to detect cells in which the PER mutation prevents proliferation, thus escaping detection by the colony assay. Expression of the mutant phenotype in the PER cells detected in the AR assay after mutagenesis with ethyl methanesulfonate (EMS) follows a pattern similar to that observed in the colony assay, reaching a maximum in 3 days, and then remaining constant for at least 4 more. After treatment with X rays (which fail to induce PER mutants in the colony assay), the frequency of PER cells detected in the AR assay also reaches a maximum on day 3, but then declines sharply, returning to the spontaneous level on day 7. In the absence of PE, the majority of the spontaneous or mutagen-induced PER cells detected in the AR assay are either incapable of dividing at all, or capable of undergoing a limited number of cell divisions to produce micro-colonies. Only few of them may continue to grow into 'full-size' colonies comparable to those detected in the colony assay. In the presence of the toxin, the proportion of PER cells which are able to divide is even smaller, and that of cells able to form full-sized PER colonies detectable in the AR assay is comparable to the results obtained in the conventional colony assay. We presume that the lethality of the PER mutations in the cells detected by the AR assay is due to abnormal protein synthesis resulting from the same mutational change that made these cells resistant to PE. While incapable of supporting colony formation, and hence detection by the colony assay, such abnormal protein synthesis still allows the detection of the mutant cells by the AR assay.

ADP Ribose Transferases↗
PubMed1991

Seasonal variation in the incidence of congenital talipes equinovarus.

A review of 77 neonates who presented with congenital talipes equinovarus over a seven-year period revealed an increase in the condition amongst babies born in the winter quarter. This finding was particularly apparent among the less severe cases of club-foot. Possible reasons for this seasonal variation are discussed.

Birth Rate↗
PubMed1989

Autoradiographic detection of mutation to exotoxin-A resistance in mouse fibroblasts treated with ethyl methanesulfonate, X-rays and ultraviolet light.

P. aeruginosa exotoxin-A (PE) blocks protein synthesis in mammalian cells by inactivating elongation factor 2 (EF-2). Toxin-resistant mutant cells can be detected autoradiographically, in cultures grown on microscope coverslips in the presence of PE, and then exposed to [3H]leucine. The frequency of PE-resistant cells detected by the autoradiographic assay in non-mutagenized cells of the established mouse cell line LTKA is 9.7 +/- 0.6 X 10(-5). Upon treatment with ethyl methanesulfonate (EMS), X-rays or ultraviolet (UV) light it increases in a dose-dependent fashion. The mutational nature of the resistance detected by the assay is indicated by its clonal inheritance, and by the dose-dependent increase in the frequency of resistant cells after mutagenesis. On the basis of the high frequency of PE-resistant cells detected by the autoradiographic assay, and their cross-resistance to diphtheria toxin (DT), we suggest that the PE-resistant mutants detected by the autoradiographic assay are of class II, i.e., they are altered in the structural gene for EF-2. The autoradiographic assay for PE resistance is similar to that for DT resistance, but is applicable also to mouse cells, which are naturally resistant to DT. Being independent of colony formation, the autoradiographic assay for PE resistance can be used with non-dividing cells, either in vitro or in vivo.

ADP Ribose Transferases↗
PubMed1987

Micronucleus formation induced in rat liver and esophagus by nitrosamines.

The rat hepatocarcinogen nitrosodimethylamine and the esophageal carcinogens nitrosomethylbenzylamine and nitrosomethylamylamine were shown to produce chromosomal damage, as manifested by micronucleus formation, in their target tissues. There was cross-reactivity in the two tissues, however, at high dose levels. Nitrosodiethylamine, which produces tumors in both the liver and esophagus in the rat, also produced micronuclei in both tissues.

Animals↗
PubMed1984

Autoradiographic assay of mutants resistant to diphtheria toxin in mammalian cells in vitro.

Diphtheria toxin kills mammalian cells by ribosylating elongation factor 2, a protein factor necessary for protein synthesis. The frequency of cells able to form colonies in the presence of the toxin can be used as an assay for mutation to diphtheria toxin resistance. We report here that resistance to diphtheria toxin can also be detected autoradiographically in cells exposed to [3H]leucine after treatment with the toxin. In cultures of Chinese hamster ovary cells, the frequency of such resistant cells is increased by exposure of the cells to gamma-rays, ultraviolet light, ethylnitrosourea, mitomycin c, ethidium bromide, and 5-bromo-2'-deoxyuridine in a dose- and time-dependent manner. The resistant cells form discrete microcolonies if they are allowed to divide several times before intoxication, which indicates that they are genuine mutants. The assay is potentially adaptable to any cell population that can be intoxicated with diphtheria toxin and labeled with [3H]leucine, whether or not the cells can form colonies. It may be useful, therefore, for measuring mutation rates in slowly growing or nondividing cell populations such as breast, brain, and liver, as well as in cells that do divide but cannot be readily cloned, such as the colonic epithelium.

Animals↗
PubMed1984

Site-specific induction of nuclear anomalies (apoptotic bodies and micronuclei) by carcinogens in mice.

The usefulness of nuclear anomalies (NA) as a short-term test for indication of carcinogens in the mouse colon has been suggested previously by experiments in which colon-specific carcinogens induced NA in the colon, whereas non-colon carcinogens were, in general, impotent in that organ. We have extended this work to other sites in the digestive tract of female C57BL/6 mice treated with gamma-rays, 1,2-dimethylhydrazine dihydrochloride, or N-methylnitrosourea. Each agent induced NA at all of the sites examined. The frequency of NA at different times after treatment depended upon both the agent used and the site examined. 1,2-Dimethylhydrazine dihydrochloride (which is known to induce tumors predominantly in the colon) induces NA with the highest efficiency (relative to gamma-rays) in the descending colon. N-Methylnitrosourea (which induces tumors mainly in the forestomach) induces NA with the highest efficiency in the forestomach. These results further support the usefulness of the assay in that the frequency of NA produced at the various sites by 1,2-dimethylhydrazine dihydrochloride and N-methylnitrosourea correlates with that found in the carcinogenicity studies.

1,2-Dimethylhydrazine↗
PubMed1983

Diurnal variation in the response of gamma-ray-induced apoptosis in the mouse intestinal epithelium.

The appearance of apoptosis has been used as an index of carcinogen-induced damage incurred by the intestinal epithelium. Here we report that the cytotoxic response elicited by gamma radiation in the duodenal and colonic epithelium of the mouse is markedly affected by the time of day at which the animals are irradiated or sampled. The diurnal pattern in radiosensitivity of the crypt cells, as measured by the appearance of apoptosis is reflective of circadian rhythms in mouse intestinal cells. Circadian effects should therefore be considered when interpreting apoptosis data obtained at one time point only or when comparing data obtained at different times of the day.

Animals↗
PubMed1980

Neighbour and temperature effects on base-analogue-induced mutation in phage T4.

The effects of neighbouring base pairs and of temperature on mutation frequencies were measured at nonsense sites in the T4rII region. 2AP-induced AT leads to GC transition frequencies are insensitive to nearest-neighbour effects, while 5BU-induced ones are promoted by GC neighbours on the 5' side. The effect of temperature on 2AP- and 5BU-induced mutation frequencies shows no simple dependence on nearest neighbours. These results are incompatible with a unitary mechanism as explanation for the effects of nearest neighbours and temperature on base-analogue-induced mutagenesis.

Base Sequence↗
PubMed1980

2-Aminopurine.

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2-Aminopurine↗
PubMed1979

Recombination in phage T4 gene-43 (DNA polymerase) mutants.

The effect of phage T4 gene 43 (DNA polymerase) mutations on recombination between adjacent base pairs was measured in rII amber and opal mutants. The mutator allele tsL56 did not promote recombination frequencies at the two sites in which its effect was studied. The antimutator allele tsCB87 caused slight or no reduction in recombination frequencies at five sites.

Alleles↗