Cytosine deaminase catalyzes the deamination of cytosine to uracil as part of the pyrimidine salvage pathway in Escherichia coli (7). The gene encoding cytosine deaminase, codA, is part of the codBA operon (3, 6). Previous mapping studies have shown that the cod operon is closely linked to the lac operon at approximately 8 min on the E. coli chromosome (4). The Kohara lambda phage clones carryi...

The DNA cis-syn cyclobutane photoproduct formed between two adjacent cytosine residues is highly mutagenic and responsible for the tandem CC to TT transition. However, its instability has prevented its in vitro study, so far. With a view to prepare oligodeoxynucleotides containing the CC cyclobutane lesion, we have synthesized in good yield a ditetrazolouracil cyclobutane dinucleotide photoprod...

The only cytosine methylase in Escherichia coli K-12 methylates the second cytosine in the sequence CC (A/T)GG and is encoded by gene dcm. Methylation and very short patch mismatch repair activities lacking in a dcm mutant of E. coli were restored by a plasmid containing the cloned dcm gene. In contrast, plasmids with the gene for EcoRII methylase, which is a homolog of dcm, restored only cytos...

After gamma irradiation of cytosine in aerated aqueous solution, yields of chemical radiation products belonging to the deamination pathway were measured. Primary stable radiolysis products, such as 5,6-dihydroxy-5,6-dihydro-uracil cis and trans forms, were present with G values lower than those obtained in the radiolysis of uracil irradiated under the same conditions. Cytosine had Gamma Irradi...

The quantum theory of atoms-in-molecules (QTAIM) in conjunction with the DFT/B3LYP/6-311++G(2d,2p) wave function are used to compute the atomic, bonded and non-bonded interactions, distributions of the charge density, ρ(r), and its Laplacian, ∇ρ(r), for the ground equilibrium structure of cytosine. The study has been further extended to include two conical intersection (CI) structures that unde...

Happiness has been viewed as a temporary emotional state (e.g., pleasure) and a relatively stable state of being happy (subjective happiness level). As previous studies demonstrated that individuals with high subjective happiness level rated their current affective states more positively when they experience positive events, these two aspects of happiness are interrelated. According to a recent...

Targeted methylation of cytosine residues by S-adenosylmethionine-dependent DNA methyltransferases modulates gene expression in vertebrates. Here we show that cytosine-5-methyltransferases catalyze reversible covalent addition of exogenous aliphatic aldehydes to their target residues in DNA, thus yielding corresponding 5-hydroxyalkylcytosines. Such atypical enzymatic reactions with non-cofactor...

We investigated systematically the effects of Tet-induced oxidation products of 5-methylcytosine on Dnmt1- and DNMT3a-mediated cytosine methylation in synthetic duplex DNA. We found that the replacement of 5-methylcytosine at a CpG site with a 5-hydroxymethylcytosine, 5-formylcytosine, 5-carboxylcytosine or 5-hydroxymethyluracil resulted in altered methylation of cytosine at both the opposite a...

It is shown that the mutagen base analogue 2-aminopurine is hydrogen-bonded at its 1-ring position when annealed with cytosine in DNA. The presence of stably hydrogen-bonded regions proximal to the 2-aminopurine-cytosine base mispair is a prerequisite for the occurrence of two hydrogen bonds coupling the bases at their 1-3- and 2-2-positions. We consider the possibility that, in the resulting h...