Biomedical subjects

S Boiteux

Publications and source records attributed to S Boiteux.

93 records · Page 6Linked to original sources

PubMedDate not supplied

Mutagenesis by alkylating agents: coding properties for DNA polymerase of poly (dC) template containing 3-methylcytosine.

After treatment of poly(dC) by the simple alkylating agent (3H)dimethylsulfate, 90 per cent of the radioactivity cochromatographied with 3-methylcytosine and 10 per cent with 5-methylcytosine which is the normally occurring methylated base. In order to study the influence of 3-methylcytosine on DNA replication, untreated and DMS-treated poly(dC) were used as templates for E. coli DNA polymerase I. The alkylation of poly(dC) inhibits DNA chain elongation, and does not induce any mispairing under high fidelity conditions. The alteration of DNA polymerase I fidelity by manganese ions allows some replication of 3-methylcytosine which mispairs with either dAMP or dTMP. Our results suggest that 3-methylcytosine could be responsible, at least partially, for the killing and the mutagenesis observed after cell treatment by alkylating agents.

Alkylating Agents↗

PubMedDate not supplied

Template properties of ultraviolet-irradiated poly(dC) replicated by E. coli DNA polymerase I: indication for a role of apyrimidinic-sites in UV-induced mutagenesis.

Ultraviolet irradiation alters the template properties of poly(dC) when replicated by Escherichia coli DNA polymerase I. These effects are due to base modifications. Some of them are identified as apurinic/apyrimidinic sites (AP-sites) by their sensitivity to AP-endonuclease B purified from Micrococcus luteus, and their template properties. The rate of formation of AP-sites in poly(dC) is estimated at 3 X 10(-7) site per nucleotide per J.m-2. Exposure of supercoiled or relaxed pBR322 DNA to UV light results also in the formation of sites sensitive to AP-endonuclease B. In this case, the rate of formation of AP-sites is the same in relaxed or supercoiled DNA: 0.3 X 10(-7) site per nucleotide per J.m-2. The apyrimidinic sites are generated through the processing of an ultraviolet induced primary lesion. We suggest that this lesion is cytosine hydrate by its rate of decay and preferential formation in single stranded DNA. Our results suggest that AP-sites might be a minor pathway leading to UV-induced mutagenesis.

Cytosine↗

PubMedDate not supplied

Base excision repair of 8-hydroxyguanine protects DNA from endogenous oxidative stress.

A particularly important stress for all cells is the one produced by reactive oxygen species (ROS) that are formed as a byproduct of endogenous metabolism or the exposure to environmental oxidizing agents. An oxidatively damaged guanine, 8-hydroxyguanine (8-OH-G), is abundantly produced in DNA exposed to ROS. The biological relevance of this kind of DNA damage has been unveiled by the study of two mutator genes in E. coli, fpg and mutY. Both genes code for DNA glycosylases that cooperate to prevent the mutagenic effects of 8-OH-G. Inactivation of any of those two genes leads to a spontaneous mutator phenotype characterized by the exclusive increase in G:C to T:A transversions. In the simple eukaryote Saccharomyces cerevisiae, the OGG1 gene encodes an 8-OH-G DNA glycosylase which is the functional homolog of the bacterial fpg gene product. Moreover, the inactivation of OGG1 in yeast creates a mutator phenotype that is also specific for the generation of G:C to T:A transversions. The presence of such system in mammals has been confirmed by the cloning of the OGG1 gene coding for a human homolog of the yeast enzyme. Human cells also possess a MutY homolog encoded by the MYH gene. Analysis of the human OGG1 gene and its transcripts in normal and tumoral tissues reveals alternative splicing, polymorphisms and somatic mutations. The aim of this review is to summarize recent findings dealing with the biochemical properties and the biological functions of 8-OH-G DNA glycosylases in bacterial, yeast, insect and mammalian cells. These results point to 8-OH-G as an endogenous source of mutations and to its likely involvement in the process of carcinogenesis.

8-Hydroxy-2'-Deoxyguanosine↗