title: 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.
abstract: 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).
mesh_terms: D001483:Base Sequence; D002250:Carbon Radioisotopes; D004256:DNA Polymerase I / Q000378:metabolism*; D004261:DNA Replication; D003845:Deoxycytosine Nucleotides / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D009691:Nucleic Acid Denaturation; D011067:Poly dA-dT / Q000096:biosynthesis*; D011089:Polydeoxyribonucleotides / Q000096:biosynthesis*; D013329:Structure-Activity Relationship; D013698:Templates, Genetic; D013942:Thymine Nucleotides / Q000378:metabolism*; D014158:Transcription, Genetic; D014316:Tritium
chemical_list: D002250:Carbon Radioisotopes; D003845:Deoxycytosine Nucleotides; D011089:Polydeoxyribonucleotides; D013942:Thymine Nucleotides; D014316:Tritium; D011067:Poly dA-dT; C041750:N(4)-methoxydeoxycytidine triphosphate; D004256:DNA Polymerase I; C024157:thymidine 5'-triphosphate