title: The effects of thioketo substitution upon uracil-adenine interactions in polyribonucleotides. Synthesis and properties of the alternating polynucleotides poly(r(A-s2U)) and poly(r(A-s2s4U)).
abstract: The polynucleotides poly[r(A-s-2U)] and poly]r(A-s2s4U)] have been synthesized and characterized by nearest-neighbour analysis, sedimentation analysis as well as spectroscopic techniques. Absorption-temperature profile and absorption-pH profile of poly[r(A-s-2U)] did not reveal a structural transition between 10 and 95 degrees C even at low ionic strength, although a variety of properties indicated a helical structure of poly[r(A-s-2U)]: remarkable hyperchromicity of the absorption spectrum, circular dichroic spectrum displaying extrema of large amplitudes, resistance against hydrolysis by ribonuclease and interaction with ethidium bromide in a manner which is characteristic of helical polynucleotides. Our results show that interactions of the type A-s-2U and A-s-2s-4U do in fact exist in helical polynucleotides. The properties of poly]r(As-2U)] furthermore demonstrate the general stabilizing effect of 2-thioketopyrimidine bases in helical polynucleotides by virtue of vertical stacking interactions with neighbouring pyrimiding and purine bases.
mesh_terms: D002942:Circular Dichroism; D004996:Ethidium / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D006868:Hydrolysis; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009994:Osmolar Concentration; D011063:Poly A-U / Q000031:analogs & derivatives*; D012260:Ribonucleases / Q000494:pharmacology; D013056:Spectrophotometry, Ultraviolet; D013455:Sulfur
chemical_list: D011063:Poly A-U; D013455:Sulfur; D012260:Ribonucleases; D004996:Ethidium