Further Studies on the Alkylation of Nucleic Acids and Their Constituent Nucleotides

Lawley, P.D.; Brookes, P.

doi:10.1042/bj0890127

Cited by 743 publications

(182 citation statements)

References 19 publications

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“…The positive charge in the base moiety and concomitant destabilization of the N-glycosidic bond were originally suggested as key features for the recognition by AlkA (64). The half-lives of the N-glycosidic bond of alkylated bases, fU and T (pH 7 and 37°C, in free deoxyribonucleosides) are 3mA (0.8 h) Ͻ 7mG (4.6 h) Ͻ O 2 ethylC (26 h) Ͻ fU (17 days) Ͻ O 2 ethylT (220 days) Ͻ O 4 ethylT ϳ T (30,65,66), where bases bearing an apparent positive charge at pH 7 are underlined (see also Fig. 8A), and the last two bases (O 4 ethylT and T) are not substrates for AlkA (63).…”

Section: Discussionmentioning

confidence: 99%

Enzymatic Repair of 5-Formyluracil

Masaoka

Terato

Kobayashi

et al. 1999

Journal of Biological Chemistry

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5-Formyluracil (fU) is a major thymine lesion produced by reactive oxygen radicals and photosensitized oxidation. We have previously shown that fU is a potentially mutagenic lesion due to its elevated frequency to mispair with guanine. Therefore, fU can exist in DNA as a correctly paired fU:A form or an incorrectly paired fU:G form. In this work, fU was site-specifically incorporated opposite A in oligonucleotide substrates to delineate the cellular repair mechanism of fU paired with A. The repair activity for fU was induced in Escherichia coli upon exposure to N-methyl-N-nitro-N-nitrosoguanidine, and the induction was dependent on the alkA gene, suggesting that AlkA (3-methyladenine DNA glycosylase II) was responsible for the observed activity. Activity assay and determination of kinetic parameters using purified AlkA and defined oligonucleotide substrates containing fU, 5-hydroxymethyluracil (hU), or 7-methylguanine (7mG) revealed that fU was recognized by AlkA with an efficiency comparable to that of 7mG, a good substrate for AlkA, whereas hU, another major thymine methyl oxidation products, was not a substrate. Cellular DNA is constantly subjected to the threat of exogenous and endogenous DNA damaging agents (1, 2). The loss of critical genetic information stored in DNA due to the damage results in lethal and mutagenic events of cells. Furthermore, it has been shown that defective processing of DNA damage, i.e. impaired DNA repair and cellular responses to DNA damage, lead to tumorigenesis and carcinogenesis (1). Reactive oxygen species generated by cellular metabolism, exogenous redox active chemicals, and ionizing radiation produce a wide spectrum of oxidative DNA base damage, which constitutes major DNA lesions induced by exogenous and endogenous DNA damaging agents (3, 4). To cope with genotoxicity associated with oxidative base damage, cells have evolved a number of repair enzymes that specifically recognize unique structural features of altered bases and remove them from DNA (1, 2, 5). Among the repair enzymes that recognize oxidative base damage from four bases, those for thymine damage have been best identified and characterized, because the chemical nature of oxidative thymine damage has been established considerably well (3, 4). Oxidative thymine lesions are classified into four groups depending on the structure: group I, C-5,C-6 hydroxylation products, such as thymine glycol and thymine hydrate; group II, ring fragmentation products, such as urea and methyltartronylurea; group III, ring contraction products, such as hydantoin derivatives; and group IV, 5-methyl oxidation products, such as 5-formyluracil (fU) 1 and 5-hydroxymethyluracil (hU). In Escherichia coli, group I products are recognized by endonucleases III and VIII (6 -10), encoded by the nth (11, 12) and nei (13, 14) genes, respectively. Recently, eukaryotic counterparts of the nth gene have been cloned, and the expressed gene products were shown to have activities similar to the E. coli enzyme (15-18). Group II lesions, such as urea resi...

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Section: Discussionmentioning

confidence: 99%

Enzymatic Repair of 5-Formyluracil

Masaoka

Terato

Kobayashi

et al. 1999

Journal of Biological Chemistry

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“…The conversion of N7-methylguanosine to 2-amino-6-hydroxy-5-methylformamido-4-ribosyl-amino-pyrimidine under alkaline conditions was described by Lawley and Brookes [20]. Under reducing alkaline conditions the same compound may be formed but since this has not been proved the conversion product is called the alkali conversion product of N7-methylguanosine.…”

Section: 8)mentioning

confidence: 99%

On the Specificity of the Reduction of Transfer Ribonucleic Acids with Sodium Borohydride

Igo‐Kemenes¹,

Zachau²

1969

Eur J Biochem

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Sodium borohydride treatment of tRNA from brewer's yeast was studied with respect to the selectivity of the reaction and to the biological functions of the modified tRNAs. The results are discussed in relation to some controversial statements in the literature.1. Borohydride treated tRNAser and tRNAPhe were digested with T i ribonuclease. By analysis of the oligonucleotide patterns it was shown that dihydrouridine and the still unknown nucleoside Y were reduced. The conversion of dihydrouridine to ureidopropanol riboside was complete under our conditions. N4-Acetylcytidine (ac4C) in position 12 of tRNAser remained unchanged while it was easily reduced as part of the trinucleotide C-ac4CC-G.2. The acceptor activity of tRNA for serine, phenylalanine, valine, tyrosine and alanine was not diminished by borohydride treatment. Also K , and Vma, were unchanged when measured with pure tRNASer and tRNAPhe and purified synthetases or with unfractionated tRNATyr.3. Acceptance of cytidine and adenosine 5'-phosphates by -C-A depleted tRNA was not impaired by borohydride reduction.4. The binding to polynucleotide or trinucleotide ribosome complexes of pure tRNASer, tRNAPhe, tRNAVa1 and tRNATyr was not changed by borohydride treatment. This is interesting particularly in the case of tRNAPhe where a modification had occurred right next to the anticodon.

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“…The mutagen originally used to isolate the nac 1 mutant was ethyl methane sulfonate (33). Mechanistically, ethyl methane sulfonate is expected to produce G/C to A/T transitions (80,81), and this expectation has been confirmed in mutagenesis studies (82)(83)(84). Thus, the C86T transition in the nac 1 Gfr gene is fully consistent with the use of ethyl methane sulfonate mutagenesis in producing the nac 1 strain.…”

Section: Discussionmentioning

confidence: 88%