title: The effect of thioketo substitution on uracil-2-aminopurine and uracil-2, 6-diaminopurine interactions in polynucleotides.
abstract: The existence of the complexes poly[r(s4U)] . poly[r(n2h6A] and poly-[r(s4U)] . poly[r(n2A)] was demonstrated by means of spectrophotometric titration and sedimentation veolicty analysis. According to the absorption-temperature profiles thioketo substitution of poly[r(U)] . poly[r(n2h6A)] led to stabilisation of the helical structure, thus implying that the 4-thioketo group does not participate in s4U . n2h6A base pairing. In the case of poly[r(s4U)] . poly[r(n2A)] drastic destabilistaion of the helical structure by thioketo substitution was observed. This indicates that the thioketo substituents participate in s4U .n2A base pairing.
mesh_terms: D001665:Binding Sites; D004926:Escherichia coli / Q000201:enzymology; D007659:Ketones; D007700:Kinetics; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D011061:Poly A; D011072:Poly U; D011119:Polynucleotides / Q000096:biosynthesis; D011117:Polyribonucleotide Nucleotidyltransferase; D011687:Purines; D013056:Spectrophotometry, Ultraviolet; D013438:Sulfhydryl Compounds; D013696:Temperature; D014498:Uracil
chemical_list: D007659:Ketones; D011119:Polynucleotides; D011687:Purines; D013438:Sulfhydryl Compounds; D011061:Poly A; D011072:Poly U; D014498:Uracil; D011117:Polyribonucleotide Nucleotidyltransferase