[Restoration of DNA supercoiling in fibroblasts in the rat subjected to gamma ray or fast neutrons].

Nucleoid sedimentation analysis was applied to the study of DNA supercoiling repair in cultured FR 3T3 fibroblasts exposed to low doses of fast neutrons or gamma-rays. Supercoiling was fully restored in both instances upon post-irradiation at 37 degrees C, but the rate of repair of neutron-induced lesions was lower than that for gamma-rays. Non-repairable breaks were not evidenced at the neutral pH used.

Unusual alkaline elution pattern induced in mammalian cell DNA by fast neutrons p(34) + Be.

Syrian hamster fibroblasts (cell line BHK 21/13) were exposed to p(34) + Be fast neutron irradiation and their DNA analysed by the alkaline elution technique. The elution profiles showed an unusual tailing off, characteristic of neutron-irradiated samples, suggesting the presence of a modification in DNA induced by the neutrons. This was not seen with 60Co gamma-irradiation.

Study of several factors in RNA-protein cross-link formation induced by ionizing radiations within 70S ribosomes of E. coli MRE 600.

The induction of RNA-protein crosslinks in E. coli 70S ribosomes by gamma-irradiation was studied by measuring the dependence of cross-link formation on ribosome concentration. The inverse dependence of cross-link percentage upon concentration up to at least 20 A260 nm units ml-1 indicate that indirect effects seem to play a more major part than direct effects for these ribosome concentrations.

[Comparison of chain breaks produced in DNA in vivo by gamma rays and neutrons; hypothesis of a new DNA radiolesion].

Using the method of alkaline elution for the treatment of cell DNA in chinese hamster fibroblasts irradiated with low doses of either cobalt-60 gamma rays or p (34 MeV) Be neutrons, we determined the kinetics of radio-induced strand breaks. The comparison gamma rays-neutrons reveals important discrepancies which suggest that neutrons induce a so for unknown reaction in DNA simultaneously with single and double strand breakage. This observation could contribute to explain the high RBE value of high LET particles.

The metabolic activation of dibenzo[a,e]fluoranthene in vitro. Evidence that its bay-region and pseudo-bay-region diol-epoxides react preferentially with guanosine.

Dibenzo[a,e]fluoranthene ( DBF ), a non- alternant carcinogenic polycyclic aromatic hydrocarbon (PAH), binds covalently to DNA. The main adducts were characterized as covalent additions of its bay-region and pseudo-bay-region diol-epoxides. The structure of these 2 adducts was analyzed by mass spectrometry using their persilyl derivatives.

Ribosomal RNA-protein cross-links, induced by gamma-irradiation of 40S and 60S ribosomal subunits of L cells.

The 40S and 60S ribosomal subunits of L cells are gamma-irradiated in the absence of oxygen at low radiation doses to keep the integrity of the ribosomal structure. We show that under these experimental conditions, specific cross-links are induced in situ between rRNA and ribosomal proteins due to close contact between their reactive groups. We found that about 15 proteins are cross-linked to the 28S RNA.

DNA-protein crosslinks induced by exposure of cultured mouse fibroblasts to dibenzo[a,e]fluoranthene and its bay- and pseudo-bay region dihydrodiols.

The presence of DNA-protein crosslinks was shown by the alkaline elution technique in cultured mouse fibroblasts treated with dibenzo[a,e]fluoranthene (DBF), a non-alternating carcinogenic PAH. The crosslinks appeared to be between DNA and protein, since the effect disappeared with proteinase treatment. The crosslinking effect increased with time of exposure to DBF.

Binding to DNA of bay region and pseudo bay region diol-epoxides of dibenzo[a,e]fluoranthene and comparison with adducts obtained with dibenzo[a,e]fluoranthene or its dihydrodiols in the presence of microsomes.

When dibenzo[a,e]fluoranthene (DBF) is incubated in vitro with mouse liver microsomes in the presence of calf thymus DNA, several metabolites bind covalently to DNA. The metabolite-nucleoside adducts were separated by h.p.

Radiochemical cross-linking between proteins and RNA within 70 S ribosomal particles from E. coli MRE600.

In the absence of oxygen, gamma-irradiation produces covalent links between some ribosomal proteins and 16 S RNA to 23 S RNA, within 70 S ribosomes from E. coli MRE600. Under optimal conditions minimizing the structural modifications induced by radiations, in situ formed cross-links appear specific and reflect close RNA-protein contacts.

Apparent stimulation of dibenzo[a,e]fluoranthene in vitro metabolism in the presence of norharman.

The effects of norharman (NH) on the metabolism of dibenzo[a,e]-fluoranthene (DBF) and on its fixation on DNA, RNA and proteins have been studied in vitro by incubation with S-9 and microsomes from rats and mice. NH causes a decrease of the activity of microsome monooxygenases proportionally to its concentration but has no effect on the activity of NADPH P-450 reductase nor on that of epoxide hydrolase. Paradoxically, the amount of DBF hydrophobic metabolites and especially that of diols and phenols, increases in the incubation mixture in the presence of NH; this increase is independent of the presence of conjugation enzymes of cytosol.

Heterocyclic polycyclic aromatic hydrocarbon carcinogenesis: 7H-dibenzo[c,g]carbazole metabolism by microsomal enzymes from mouse and rat liver.

The metabolism of dibenzo[c,g]carbazole (DBC), was studied in vitro using microsomal fractions of mouse and rat liver from animals, which were treated with 3-methylcholanthrene (MC). The separation of extractable metabolites by high pressure liquid chromatography (HPLC) and thin-layer chromatography (TLC) as well as identification of most of them by nuclear magnetic resonance, mass spectrometry and comparison with synthetically obtained products are described. The microsomes of both species produced the same twelve compounds of which the following have been identified: five monohydroxylated derivatives (phenols), the product of further oxidation of one of them, and a dihydrodiol.

Radiochemical cross-linking of proteins to RNA within ribosomal subunits from E. colil MRE 600.

Irradiation in vitro of 30S and 50S ribosomal subunits from E. coli MRE 600 by gamma rays from cobalt 60, in the absence of oxygen, results in the formation of covalent links between the RNAs and some ribosomal proteins. At low radiation doses, just sufficient to keep the integrity of the ribosome structure, the phenomenon appears highly specific.

Binding of dibenzo(a,e)fluoranthene, a carcinogenic, polycyclic hydrocarbon without K-region, to nucleic acids in a subcellular microsomal system.

Dibenzo(a,e)fluoranthene (DBF), a highly carcinogenic polycyclic hydrocarbon without an apparent K-region, binds covalently to DNA, transfer RNA, and polyribonucleotides when incubated with hepatic microsomal fractions under standard conditions. Optimal binding conditions for [3H]DBF were established. Methylcholanthrene-pretreated mouse liver microsomes induced a higher level of binding of [3H]DBF to DNA than did similarly induced rat liver microsomes.

Biochemical analysis of damage induced in yeast by formaldehyde. II. Induction of cross-links between DNA and protein.

Exposure of Saccharomyces cerevisiae cells to formaldehyde-induced cross-links between DNA and proteins. This damage was demonstrated by three different techniques. Ultraviolet irradiation also produced cross-links between DNA and proteins in yeast.

Biochemical analysis of damage induced in yeast by formaldehyde. I. Induction of single-strand breaks in DNA and their repair.

Analysis of sedimentation profiles in alkaline sucrose gradients showed that, through a metabolic process, formaldehyde (FA) produced single-strand breaks in DNA of exponential phase cells of haploid wild-type Saccharomyces cerevisiae. The production of this type of lesion was dose-dependent. Strains defective in excision-repair of pyrimidine dimers induced by ultraviolet (UV) irradiation showed a reduced capacity to undergo single-stand breaks after treatment with FA.

[Formation of covalent linkages between the nucleic acid and protein constituents of E. coli MRE 600 ribosomes during gamma irradiation].

Gamma-irrdiation of E. coli MRE 600 ribosomes in aqueous suspensions leads to covalent linkages between the RNA and some ribosomal proteins. The presence of oxygen during the irradiation strongly inhibits this phenomenon.

[Formation, by gamma irradiation, of RNA-protein cross-links in E. coli ribosomes].

Gamma irradiation in desaerated conditions of E. coli MRE 600 ribosomes, labelled with C14 uracil, leads to a decrease of extractibility of C14 RNA by lithium chloride 4 M-urea 8 M. On the other hand, the radioactivity of the protein fraction increases with irradiation.