title: Salt induced transitions between multiple conformations of poly (rG-m5dC).poly (rG-m5dC).
abstract: Salt induced transitions between four conformations of the methylated ribo-deoxyribo co-polymer poly (rG-m5dC).poly (rG-m5dC) have been studied using phosphorous-NMR, Raman spectroscopy, and circular dichroism. A high salt A-Z transition is observed for the polymer. However, the methylated polymer does not enter the high salt Z form more readily than the analogous unmethylated polymer, unlike the effect of methylation on the fully deoxy polymer poly (dG-dC).poly (dG-dC). The methylated polymer fails to undergo a low salt A-Z transition in 5 mM Tris buffer, unlike the unmethylated poly (rG-dC).poly (rG-dC). However, if the counterion is changed to triethanolamine buffer, an A-Z transition does take place. In 5 mM Tris buffer the phosphorous-NMR spectrum of poly (rG-m5dC).poly (rG-m5dC) shows one resonance in the absence of NaCl that splits into two closely spaced resonances as the NaCl level is increased to 30 mM. The Raman spectrum of poly (rG-m5dC).poly (rG-m5dC) shows that it is in the A conformation at intermediate salt concentrations. From this we conclude that poly (rG-m5dC).poly (rG-m5dC) is in a regular A conformation in Tris buffer at low Na+ levels, shifting to an alternating A conformation with a dinucleotide repeat at intermediate salt concentrations.
mesh_terms: D002942:Circular Dichroism / Q000379:methods; D004926:Escherichia coli / Q000235:genetics; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D009690:Nucleic Acid Conformation; D009994:Osmolar Concentration; D010957:Plasmids; D011089:Polydeoxyribonucleotides; D011119:Polynucleotides; D012492:Salts; D013059:Spectrum Analysis, Raman / Q000379:methods; D013329:Structure-Activity Relationship
chemical_list: D011089:Polydeoxyribonucleotides; D011119:Polynucleotides; D012492:Salts; C043827:poly(rG-dC).poly(rG-dC)