Poly(pyrimidine) . poly(purine) synthetic DNAs containing 5-methylcytosine form stable triplexes at neutral pH.
Poly(pyrimidine) . poly(purine) tracts have been discovered in the 5'-flanking regions of many eucaryotic genes. They may be involved in the regulation of expression since they can be mapped to the nuclease-sensitive sites of active chromatin. We have found that poly(pyrimidine) . poly(purine) DNAs which contain 5-methylcytosine (e.g. poly[d(Tm5C)] . poly[d(GA)]) will form a triplex at a pH below 8. In contrast, the unmethylated analogue, poly[d(TC)] . poly[d(GA)] only forms a triplex at pHs below 6. Synthetic DNAs containing repeating trinucleotides and poly[d(Um5C)] . poly[d(GA)] behave in a similar manner. Thus the stability of a triplex can be controlled by methylation of cytosine. This suggests a model for the regulation of expression based upon specific triplex formation on the 5'-side of eucaryotic genes.
D044503:5-Methylcytosine; D003596:Cytosine / Q000031:analogs & derivatives*; D004247:DNA / Q000138:chemical synthesis*; D004355:Drug Stability; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents; D009691:Nucleic Acid Denaturation; D011089:Polydeoxyribonucleotides / Q000138:chemical synthesis*; D012091:Repetitive Sequences, Nucleic Acid; D013050:Spectrometry, Fluorescence; D013329:Structure-Activity Relationship; D013816:Thermodynamics
D007202:Indicators and Reagents; D011089:Polydeoxyribonucleotides; C051802:triplex DNA; D044503:5-Methylcytosine; D003596:Cytosine; D004247:DNA