Deprotection of methylphosphonate oligonucleotides with ethylenediamine was evaluated in a model system. Methylphosphonate sequences of the form 5'-TTTNNTTT, where N was either N4-bz-dC, N4-ibu-dC, N2-ibu-O6-DPC-dG, N2-ibu-dG, N6-bz-dA, or T, were used to determine the extent of modifications that occur during deprotection. Up to 15% of N4-bz-dC was found to transaminate at the C4 position when...

AGT (O6-alkylguanine DNA alkyltransferase) is an important DNA-repair protein that protects cells from killing and mutagenesis by alkylating agents. The AGT genes from two extremely thermophilic organisms, the bacterium Aquifex aeolicus and the archaeon Archaeoglobus fulgidus were PCR-derived and cloned into an expression vector. The nucleotide sequence of the Aq. aeolicus AGT encodes a 201-ami...

DNA mismatch repair (MMR) sensitizes human and Escherichia coli dam cells to the cytotoxic action of N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) while abrogation of such repair results in drug resistance. In DNA methylated by MNNG, MMR action is the result of MutS recognition of O6-methylguanine base pairs. MutS and Ada methyltransferase compete for the MNNG-induced O6-methylguanine residues, a...

Intrinsic or acquired chemoresistance to alkylating agents is a major cause of treatment failure in patients with malignant brain tumors. Alkylating agents, the mainstay of treatment for brain tumors, damage the DNA and induce apoptosis, but the cytotoxic activity of these agents is dependent on DNA repair pathways. For example, O6-methylguanine DNA adducts can cause double-strand breaks, but t...

The effects of fat content and nitrite-curing of pork were investigated on the formation of cytotoxic and genotoxic lipid oxidation products (malondialdehyde, 4-hydroxy-2-nonenal, volatile simple aldehydes), protein oxidation products (protein carbonyl compounds) and NOC-specific DNA adducts (O6-carboxy-methylguanine) during in vitro digestion. The formation of these products during digestion i...

Myelosuppression is the dose-limiting toxicity for nitrosourea chemotherapy. This toxicity predominantly involves modification of the O6 position of guanine with an alkyl moiety. The enzyme responsible for repair of O6-alkylguanine adducts, O6-alkylguanine-DNA alkyltransferase (alkyltransferase), is expressed at low levels in bone marrow (BM) cells. High alkyltransferase expression prevents the...

The GacS/GacA system in the root colonizer Pseudomonas chlororaphis O6 is a key regulator of many traits relevant to the biocontrol function of this bacterium. Proteomic analysis revealed 12 proteins were down-regulated in a gacS mutant of P. chlororaphis O6. These GacS-regulated proteins functioned in combating oxidative stress, cell signaling, biosynthesis of secondary metabolism, and secreti...

Pretreatment of H4 (rat hepatoma) cells for 48 hr with low nontoxic doses of alkylating agents [methyl methanesulfonate (MMS), N-methyl-N'-nitro-N-nitrosoguanidine (MNNG), and N-methyl-N-nitrosourea] renders the cells more resistant to the toxic effect of these compounds. Crossreactivity for survival is also observed with the different alkylating agents tested. Pretreatment with MNNG enables th...

We examined the relationship between serotype and cytotoxic necrotizing factor (CNF) production in 123 hemolytic strains of Escherichia coli isolated from both stools and extraintestinal infections. Of 76 strains producing both hemolysin (Hly) and CNF, 66 (87%) belonged to one of six serogroups (O2, O4, O6, O22, O75, and O83). In contrast, 47 E. coli strains producing Hly only belonged to 21 di...

High levels of expression of the DNA repair enzyme O6-alkylguanine DNA-alkyltransferase (OGAT) (EC 2.1.1.63) account for tumor cell resistance to methylating agents. Previous studies suggested that methylating triazenes might have a potential role for the treatment of acute leukemias with low levels of OGAT. In the current study, we transduced the human OGAT cDNA in OGAT-deficient leukemia cell...