Ring-opened 7-methylguanine nucleotides are resistant to nuclease P1 digestion and good substrates to polynucleotide kinase

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Abstract
Dimethyl sulfate was used to prepare 7-methyl-2′-deoxy-guanosine 3′-monophosphate (7-methyl-dGMP), whkh was ring-opened in alkali to 2′-deoxy-N5-methyl-N5-formyl-2,5,6-triamino4-oxopyrimidine 3′-monophosphate (ROM-dGMP). ROM-dGMP was not dephosphorylated by nuclease P1 in contrast to normal deoxynucleotides. It was efficiently 5′-phosphorylated by T4 polynucleotide kinase. When methylated DNA was alkali-treated and digested with mkro-coccal nuclease, spleen phospbodiesterase and nuclease P1, ROM-dGMP was formed and this was labeled with [γ-32P]-ATP hi the presence of polynucleotide kinase. Ring-opening and P1 treatment appear methods of choice for 32P-post-labeUng of 7-alkylguanines in DNA.
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