title: Unusual contribution of 2-aminoadenine to the thermostability of DNA.
abstract: The poly(dA-dU) and poly(dI-dC) duplexes have very similar thermostabilities (Tm). This similarity extends also to the pyrimidine 5-methyl group-containing poly(dA-dT) and poly(dI-m5dC). The differences between chemical structures of the A:U and I:C or the A:T and I:m5C base-pairs seem to be unimportant for the thermostability of the DNA. However, on the insertion of an amino group into position 2 of the purines the similarities disappear. Thermostabilities of poly(n2dA-dU) and poly(dG-dC) as well as the poly(n2dA-dT) and poly(dG-m5dC) are radically different. This is also the case with their other 5-substituted pyrimidine-containing derivatives, the 5-ethyl, 5-n-butyl and 5-bromo analogues. The G:C-based polynucleotides are more stable by an average of 40 degrees C than the n2A.U-based ones. Poly(dA,n2dA-dT)-s containing various proportions of A and n2A as well as the natural DNA of S-2L cyanophage that contains n2A bases instead of A were also studied. It was found that dependence of Tm on the n2A-content was non-linear and that the lower Tm is not the consequence of a particular nucleotide sequence. The possible structural reasons for the lower thermostabilization of these B-DNAs by the n2A:T base-pair as compared to the G:C are discussed.
authors.affiliation: Central Research Institute for Chemistry, Hungarian Academy of Sciences, Budapest, Hungary. Janos_Sagi@macmail.lbl.gov
authors.forename: J
authors.initials: J
authors.lastname: Sági
authors.forename: E
authors.initials: E
authors.lastname: Szakonyi
authors.forename: M
authors.initials: M
authors.lastname: Vorlícková
authors.forename: J
authors.initials: J
authors.lastname: Kypr
mesh_terms: D015075:2-Aminopurine / Q000031:analogs & derivatives* / Q000737:chemistry; D000042:Absorption; D001435:Bacteriophages / Q000737:chemistry; D001482:Base Composition; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D003854:Deoxyribonucleotides / Q000737:chemistry; D015394:Molecular Structure; D009690:Nucleic Acid Conformation; D009692:Nucleic Acid Heteroduplexes; D011687:Purines / Q000737:chemistry; D011743:Pyrimidines / Q000737:chemistry; D013329:Structure-Activity Relationship; D014466:Ultraviolet Rays
chemical_list: D003854:Deoxyribonucleotides; D009692:Nucleic Acid Heteroduplexes; D011687:Purines; D011743:Pyrimidines; D015075:2-Aminopurine; C007300:2,6-diaminopurine; D004247:DNA; C030986:pyrimidine; C030985:purine