Human lymphoblastoid cell lines from normal individuals and from patients with ataxia telangiectasia were either proficient or deficient in their ability to repair the mutagenic DNA adduct O6-methylguanine that is induced by methylating carcinogens. There was no relationship between the capacity to repair O6-methylguanine and the ataxia telangiectasia phenotype. Time-course studies done followi...

DNA repair of O6-alkylguanine by O6-alkylguanine-DNA alkyltransferase (06-AT) may be crucial in modulating the extent of cytogenetic damage induced by 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), an important anticancer chemotherapeutic agent. To test this idea we treated normal human lymphocytes for 1 h with methylnitrosourea (MNU), which inactivates O6-AT, and then treated them for 1 h with B...

The capacity to repair O6-methylguanine-DNA adducts was measured in the liver of transgenic mice expressing a chimeric gene consisting of the inducible P-enolpyruvate carboxykinase (GTP) promoter linked to the bacterial O6-alkylguanine-DNA alkyltransferase (ada) gene. Under induced conditions, total hepatic alkyltransferase reached 32.8 +/- 4.2 (SE) fmol/micrograms DNA compared to 7.8 +/- 1.1 f...

Double-stranded (ds) oligodeoxynucleotides (29mers) containing an O6-ethylguanine (O6-EtGua) flanked 5' and 3' by different bases (5'..TGT..3'; 5'..CGG..3', 5'..GGT..3'; 5'..GGG..3'; 5'..GGA..3') were synthesized to investigate the binding and repair characteristics of recombinant human O6-alkylguanine-DNA alkyltransferase (AT) in vitro. The apparent association constant (KA(app)) of AT to the ...

O6-Alkylguanine-DNA alkyltransferase partially purified from cultured human lymphoblasts (CEM-CCRF line) was inactivated with DNA substrates that had been treated separately with five methylating agents or with five chloroethylnitrosoureas. The extent of depletion of the transferase by alkylated DNA was compared with its inactivation by direct reaction with these ten agents. As expected, DNA su...

Previous studies have shown that chronic treatment of rats with dimethylnitrosamine (DMN) (2 mg/kg for 3 weeks) results in increased repair of O6-methylguanine (O6-mGua) in liver DNA. The experiments reported here try to determine if this increased repair is confined to one or more cell populations of the liver. Liver cells [parenchymal (PC) and nonparenchymal (NPC)] were separated by elutriati...

Alkylating agents react with various nitrogen and oxygen atoms in DNA and many of the products are substrates for repair processes. Oxygen atom derivatives such as O6-methylguanine (O6-meG) O4-methylthymine and methylphosphotriesters (MP) have been shown to undergo repair by methyl group removal. The proteins involved in the latter reaction can be considered to be methyltransferases (MT) becaus...

Cytotoxicity of methylating agents is caused mostly by methylation of the O6 position of guanine in DNA to form O6-methylguanine (O6-meG). O6-meG can direct misincorporation of thymine during replication, generating O6-meG:T mismatches. Recognition of these mispairs by the mismatch repair (MMR) system leads to cell cycle arrest and apoptosis. MMR also modulates sensitivity to other antitumor dr...

An impressive array of evidence has been obtained during the past decade establishing correlations between specific DNA adducts and carcinogenesis. Many of the studies utilized organ specific differences in carcinogenesis to establish the correlations. More recently, we have investigated similar relationships between target and nontarget cell populations within the liver. Chronic exposure to me...

Mammary and skin tumors induced in rodents by N-methyl-N-nitrosourea treatment have a G:C to A:T transition mutation in codon 12 of H-ras, probably resulting from alkylation of O6 of guanine by the carcinogen. This codon contains two guanines (5'-GGA-3'), but mutations are observed only in the central base pair of this codon. The same selectivity for mutations of -GGA-sequences has also been ob...