Two rotameric forms of open ring 7-methylguanine are present in alkylated polynucleotides.
High performance liquid chromatography analysis of imidazole open ring 7-methylguanine, 2-6 diamino-4-hydroxy-5N-methyl-formamidopyrimidine (rom7G), showed two well-separated peaks (fI and fII) of the same magnitude. Rechromatography of each isolated component indicated that they are slowly interconverted to give a 1:1 mixture. NMR analysis demonstrated that the two species observed on reversed phase HPLC are rotational isomers. Thermodynamic measurements strongly suggested that the equilibrium can be assigned to rotation around the N-methyl formamido bond. The two species, fI and fII, separated by HPLC were identified as rotamers E and Z, respectively. The structures of fI and fII were also determined. A polynucleotide containing rom7G was obtained by alkaline treatment of poly (dGC) containing 7-methylguanine. In order to study its structure within the polynucleotide, rom7G was enzymatically excized by E.coli rom7G-DNA glycosylase. The analysis of the products released by the enzyme showed a 1:4 mixture of the two rotamers favoring the Z form (fII).
D000478:Alkylation; D002851:Chromatography, High Pressure Liquid / Q000379:methods; D006147:Guanine / Q000031:analogs & derivatives* / Q000302:isolation & purification; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D009690:Nucleic Acid Conformation; D011089:Polydeoxyribonucleotides; D013237:Stereoisomerism
D011089:Polydeoxyribonucleotides; C019530:poly(dC-dG); D006147:Guanine; C008450:7-methylguanine