Guanine residues

Jones et al.S0, sl synthesized a guanine derivative of cellulose, 29 (G-Cellulose), and found that the affinity of biosynthetic polynucleotides for the cellulose is in the order, poly C > Poly A > Poly U. They claimed that hydrogen-bonding between guanine residues and Poly C was probably taking place. 

Cross-linkage - bifunctional agents may form covalent bonds with each of two adjacent guanine residues and such inter-strand cross-links will lead to inhibition of DNA replication and transcription. Intra-strand and DNA-protein cross-links may also be formed ... 

Depurination - N7 alkylation may cause cleavage of the imidazole ring and excision of the guanine residue, leading to DNA strand breakage. 

The inhibitors of RNA polymerase, which generates RNA from DNA, inhibit a crucial step in gene expression. Inhibition of the eukaryotic form of RNA polymerase is used in cancer chemotherapy and is also an important experimental tool. For example, actinomy-cin D binds to the guanine residues in DNA and blocks the movement of the eukaryotic RNA polymerase. Specific inhibitors of bacterial RNA polymerase can be used as antibacterial agents. Most of these inhibitors like rifamycin bind to the prokaryotic enzyme. 

Several studies (for reviews, see Steenken, 1989 Diz-daroglu, 1991) had already shown that OH reacts in a multiplicity of ways with all four DNA bases. Thus, OH can add to guanine residues at C4, C5 and C8 positions to give hydroxyguanine radicals that can have various fates. For example, addition of OH to C8 of guanine produces a radical that can be reduced... 

Devasagayam, T.P.A., Steenken, S., Obendorf, M.S.W., Schultz, W.A. and Sies, H. (1991). Formation of 8-hydroxy(deoxy)guanosine and generation of strand breaks at guanine residues in DNA by singlet oxygen. Biochemistry 30, 6283-6289. 

Analogous to the well-studied acid-catalyzed deglycosylation of guanine residues from the loss of alkylated bases from the sugar-phosphate backbone likely... 

There are examples in which base radicals undergo reaction with adjacent base residues. The 5-(2 -deoxyuridinyl)methyl radical (63, Scheme 8.30) can forge an intrastrand cross-link with adjacent purine residues. Cross-link formation is favored with a guanine residue on the 5 -side of the pyrimidine radical and occurs under low-oxygen conditions. A mechanism was not proposed for this process, but presumably the reaction involves addition of the nucleobase alkyl radical to the C8-position of the adjacent purine residue. Molecular oxygen likely inhibits crosslink formation by trapping the radical 63, as shown in Scheme 8.24. The radical intermediate 89 must undergo oxidation to yield the final cross-linked product 90,... 

Relevant kinetic information on two competitive reactions of guanine radical cations within double stranded DNA, namely hydration and hole transfer to another guanine residue, has been examined [13]. Thus, the pseudoorder rate for hydration of guanine radical cations 38 has been estimated to... 

In Z-DNA, guanine residues are syn, whereas cytosine and thymine residues are anti. Eukaryotic DNA contains several alternating purine-pyrimidine sequences consistent with die Z-DNA conformation however, the biologic significance of Z-DNA is still unclear. 

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