title: Evidence for sequence-specific conformational changes in DNA from the melting temperatures of DNA phosphorothioate derivatives.
abstract: Analogs of alternating purine-pyrimidine DNA polymers such as poly(dA-dT)-poly(dA-dT) can be made with phosphorothioate groups in the DNA backbone. A phosphorothioate diester at the 5'-purine-pyrimidine-3' step causes a significant lowering of the polymer's melting temperature compared to a phosphorothioate diester at the 5'-pyrimidine-purine-3' step. This may occur because sulfur substitution increases anionic charge density in the DNA minor groove and 5'-purine-pyrimidine-3' steps narrow the minor groove. The ability to modulate charge density in the DNA backbone via sulfur substitution should prove useful in studies of sequence-dependent conformational changes in DNA.
mesh_terms: D003460:Crystallization; D004247:DNA; D006358:Hot Temperature; D009682:Magnetic Resonance Spectroscopy; D009690:Nucleic Acid Conformation; D009692:Nucleic Acid Heteroduplexes; D063086:Organothiophosphates; D009946:Organothiophosphorus Compounds; D011067:Poly dA-dT / Q000378:metabolism; D011759:Pyrrolidines / Q000378:metabolism; D012996:Solutions; D013329:Structure-Activity Relationship; D013816:Thermodynamics
chemical_list: D009692:Nucleic Acid Heteroduplexes; D063086:Organothiophosphates; D009946:Organothiophosphorus Compounds; D011759:Pyrrolidines; D012996:Solutions; D011067:Poly dA-dT; C004861:dipyrandium; D004247:DNA