Replication and demethylation of 0/sup 6/-methylguanine in DNA
O/sup 6/-Methylguanine, produced in DNA by simple alkylating carcinogens, is considered to be the primary mutagenic Lesion and is implicated in carcinogenesis induced by these agents. Its ultimate biological effect is determined both by its persistence in DNA and by its miscoding potential during replication and transcription. Polydeoxynucleotides containing O/sup 6/-methylguanine were synthesized for use as substrates for repair enzymes and as templates for DNA polymerases. Replication was carried out with T5 phage DNA polymerase under standard condition. The removal of m/sup 6/ dG from DNA in mammalian cells is similar to the repair pathway previously established for E. coli in that (1) demethylation of m/sup 6/dG occurs in situ without alteration or removal of the resulting guanine residue, (2) the enzyme repair appears to react stoichiometrically with the substrate, and (3) it appears that the expression of the methyl transferase activity is under regulatory control. Levels of the activity were found to vary widely in mammalian cells. Incorporation of m/sup 6/dG during DNA synthesis may be a significant factor in the mutagenesis caused by this agent. The base-pairing properties of m/sup 6/dG during in vitro DNA replication support the proposed role of m/sup 6/dG in the mutagenesis caused by alkylating carcinogens in vivo. O/sup 6/-Methylguanine base pairs preferentially with thymine during DNA synthesis leading to GC ..-->.. AT transition mutation. However, dT and dC act as competitive inhibitors during incorporation opposite m/sup 6/dG, therefore, the mutagenic potential of m/sup 6/dG is dependent on the relative intracellular concentrations of these precursors. Different DNA polymerases recognize m/sup 6/dG differently depending on whether it is a substrate (m/sup 6/dGTP) or in the template (m/sup 6/dG) for DNA replication. The relative mutagenic potentials of m/sup 6/dGTP and m/sup 6/dG in the cell are therefore dependent on the cell type as well as on the concentration of the substrates. (ERB)
- Research Organization:
- Oak Ridge National Lab., TN (USA); Tennessee Univ., Oak Ridge (USA). Graduate School of Biomedical Sciences
- DOE Contract Number:
- W-7405-ENG-26
- OSTI ID:
- 5237391
- Report Number(s):
- CONF-820439-3; ON: DE82017530
- Country of Publication:
- United States
- Language:
- English
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Base-pairing properties of O/sup 6/-methylguanine in template DNA during in vitro DNA replication
Mutagenic properties of O/sup 6/-methylguanine in DNA in vivo and in vitro
Related Subjects
550400 -- Genetics
560301* -- Chemicals Metabolism & Toxicology-- Cells-- (-1987)
59 BASIC BIOLOGICAL SCIENCES
63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
ALKYLATING AGENTS
AMINES
ANIMAL CELLS
BIOLOGICAL EFFECTS
BIOLOGICAL PATHWAYS
BIOLOGICAL RECOVERY
BIOLOGICAL REPAIR
CARCINOGENS
CHEMICAL REACTIONS
DNA
DNA REPLICATION
ENZYME ACTIVITY
ENZYMES
GUANINE
HETEROCYCLIC COMPOUNDS
HYDROXY COMPOUNDS
METHYLATION
MUTAGENESIS
NUCLEIC ACID REPLICATION
NUCLEIC ACIDS
NUCLEOTIDYLTRANSFERASES
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOSPHORUS-GROUP TRANSFERASES
POLYMERASES
PURINES
RECOVERY
REPAIR
SUBSTRATES
TRANSFERASES