title: 7-Methylguanine in poly(dG-dC).poly(dG-dC) facilitates z-DNA formation.
abstract: Poly(dG-dC).poly(dG-dC) was methylated at the N-7 position of guanine through the use of dimethyl sulfate. The conversion of poly(dG-dC).poly(dG-dC) from B-DNA to the Z-DNA form was followed by measuring both the circular dichroic spectra and changes in the absorbance ratio A295/A260. Increasing methylation steadily decreases the amount of NaCl or MgCl2 that is required to convert the polymer from B-DNA to Z-DNA. At 100% methylation of the guanine residues, the modified polymer is fully converted to Z-DNA in a physiological salt solution. Kinetic experiments show that methylation markedly accelerates the speed of the conversion from B-DNA to Z-DNA in the presence of added salt. These effects may be partly due to the positive charge on guanine that accompanies N-7 methylation.
mesh_terms: D001483:Base Sequence; D002942:Circular Dichroism; D004247:DNA; D006151:Guanosine / Q000031:analogs & derivatives; D008745:Methylation; D009690:Nucleic Acid Conformation; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship
chemical_list: D006151:Guanosine; C016578:7-methylguanosine; D004247:DNA