N4-Methoxydeoxycytidine triphosphate is in the imino tautomeric form and substitutes for deoxythymidine triphosphate in primed poly d[A-T] synthesis with E. coli DNA polymerase I

Nucleic Acids Res. 1984 Jun 11;12(11):4609-19. doi: 10.1093/nar/12.11.4609.


N4- Methoxydeoxycytidine triphosphate ( mo4dCTP ) substitutes for dTTP in poly d[A-T] synthesis with E. coli DNA polymerase I (Pol I). In parallel experiments using as template-primer, poly d[G-C], no incorporation of [14C] mo4dC was detected. This indicates that this deoxy derivative acts as the imino tautomer, as previously found for the riboderivative . Nearest neighbor analysis of transcripts of poly d[A-T] containing mo4dC shows that the derivative substitutes for only one base. In replication, singlestranded mo4dC -containing polymers gave little misincorporation, including that of dATP which can hydrogen-bond to mo4dC in the imino form, if the methoxy group is anti to the N-3. It is therefore assumed that the methoxy group is constrained anti in a polymer such as d[A-T], but can be in the syn form in singlestranded polymers and not recognized by DNA polymerase. mo4dC destabilizes the poly d[A-T] helix, as indicated by a lowered and less cooperative melting. Steric factors such as adjacent base displacement were invoked for similar findings with the doublestranded r( U61 , mo4C39 ) X r(A).

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Base Sequence
  • Carbon Radioisotopes
  • DNA Polymerase I / metabolism*
  • DNA Replication
  • Deoxycytosine Nucleotides / metabolism*
  • Escherichia coli / enzymology*
  • Nucleic Acid Denaturation
  • Poly dA-dT / biosynthesis*
  • Polydeoxyribonucleotides / biosynthesis*
  • Structure-Activity Relationship
  • Templates, Genetic
  • Thymine Nucleotides / metabolism*
  • Transcription, Genetic
  • Tritium


  • Carbon Radioisotopes
  • Deoxycytosine Nucleotides
  • Polydeoxyribonucleotides
  • Thymine Nucleotides
  • Tritium
  • Poly dA-dT
  • N(4)-methoxydeoxycytidine triphosphate
  • DNA Polymerase I
  • thymidine 5'-triphosphate