Guanine-rich DNA

Temozolomide undergoes spontaneous hydrolysis and decarboxylation at physiological pH value and thereafter a methyldiazonium ion is released. This ion forms DNA adducts within guanine rich DNA sequences. Temozolomide has high bioavailability and is metabolized in the liver. 

The photo-induced charge conduction mechanism in double-strand guanine-rich DNA-based molecules, and AT pairs attenuating the conductivity by off-resonance superexchange steps is broadly supported. Mechanistic mapping has been based on both direct charge transfer kinetics in the nano-, pico- and femtosecond ranges... 

The drug exerts its action by getting itself boimd to guanine-rich DNA and thereby helps in inhibiting DNA-dependent RNA polymerase. It predominantly acts during the S-phase. As it is found... 

Li, T., Du, Y., Li, B. L., Dong, S. J. (2007c). CE with electrochemical detection for investigation of label-free recognition of amino acid amides by guanine-rich DNA... 

Certain guanine-rich DNA sequences readily fold into the four-stranded stmc-tures formed by stacked arrays of guanine quartets (or tetrads) - square planar arrangements of four guanine bases coimected by Hoogsteen-type hydrogen bonds (Fig. 6.1). 

EXPLORING THE STRUCTURAL REPERTOIRE OF GUANINE - RICH DNA SEQUENCES COMPUTER MODELLING STUDIES... 

Telomeres are the nucleoprotein assembUes at the ends of chromosomes that comprise guanine-rich tandem-repeating DNA sequences (the size of a typical telomere is aroimd 6-12 kb in length in hiunans) together with a number of structural and regulatory proteins. The major function of telomeres is to protect chromosome ends from base-pair loss and end-to-end fusions, thereby safeguarding the integrity of each chromosome [10, llj. The enzyme... 

Protected amino acid peptides are also conjugated to guanine rich oligonucleotides using EDC. For example, the N-protected amino acid 674 reacts with H2N DNA (DNA = GGTGG where T is modified deoxyuridine) in the presence of EDC to give the amide 675. °... 

A series of 7-alkynylamino-7-deaza-dG analogues was examined for their ability to stabilise DNA duplexes. As the length of the alkynyl chain increases, duplex stability decreases. The incorporation of 7-deaza-8-aza-dG residues into guanine-rich sequences reduces the formation of guanine quartets due to the inability to form Hoogsteen base pairs. The N -glycosylated 7-deaza-8-aza-dG derivative (90) forms stable base pairs with iso-dC in antiparallel duplexes and with dC in parallel duplexes, but does not form guanine quartet... 

Figure 5 Cross-peaks in homonuclear 2D TOCSY spectra arising due to ROESY effects. Clean TOCSY spectra were acquired with the MLEV-17 spin-lock sequence, (a) Base proton H6-to-methyl correlations in a 27-nt AT-rich DNA stem-loop structure 93 the spectrum was recorded with the 50-ms mixing sequence, (b) and (c) TOCSY spectra acquired for a 31 -nt stem-loop RNA (unpublished data), (b) H5-H6 cross-peaks in pyrimidines and a H1 -H8 cross-peak (boxed) in the syn guanine from the tetraloop UACG the spectrum was recorded with the 30-ms mixing sequence, (c) Sequential H2 -H6/H8 cross-peaks the spectrum was recorded with the 90-ms mixing sequence.

R192 D. J. Patel, S. Bouaziz, A. Kettani and Y. Wang, Structures of Guanine-Rich and Cytosine-Rich Quadruplexes Formed in Vitro by Telomeric, Centromeric, and Triplet Repeat Disease DNA Sequences , p. 389... 

Temozolomide is an imidazotetrazine derivative. Temozolo-mide is a prodrug that undergoes rapid nonenzymatic conversion to the reactive compound MTIC. Cytotoxicity and antiproliferative activity against tumor cells are thought to be primarily caused by alkylation (methylation) of specific guanine-rich areas of DNA that initiates transcription. It is indicated for refractory anaplastic astrocytoma and treatment of newly diagnosed glioblastoma multiforme concomitantly with radiotherapy and then as maintenance treatment. 

The i-motif can be formed from a cytosine-rich strand with protonation of the intercalated C-C base pairs [Figure 13(a)]. In the case of duplex DNA the disassociation of the cytosine and guanine-rich strands is required before being refolded into a C-rich i-motif and a G-rich G-quadruplex motif. Under normal physiological cellular conditions the guanine and its complimentary sequences... 

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