title: CD of homopolymer DNA-RNA hybrid duplexes and triplexes containing A-T or A-U base pairs.
abstract: CD spectra and difference-CD spectra of (a) two DNA X RNA hybrid duplexes (poly[r(A) X d(U)] and poly[r(A) X d(T)]) and (b) three hybrid triplexes (poly-[d(T) X r(A) X d(T)], poly[r(U) X d(A) X r(U)], and poly[r(T) X d(A) X r(T)]) were obtained and compared with CD spectra of six A X U- and A X T-containing duplex and triplex RNAs and DNAs. We found that the CD spectra of the homopolymer duplexes above 260 nm were correlated with the type of base pair present (A-U or A-T) and could be interpreted as the sum of the CD contributions of the single strands plus a contribution due to base pairing. The spectra of the duplexes below 235 nm were related to the polypurine strands present (poly-[r(A)] or poly[d(A)]). We interpret the CD intensity in the intermediate 255-235 nm region of these spectra to be mainly due to stacking of the constituent polypurine strands. Three of the five hybrids (poly[r(A) X d(U)], poly[r(A) X d(T)], and poly[d(T) X r(A) X d(T)]) were found to have heteronomous conformations, while poly[r(U) X d(A) X r(U)] was found to be the most A-like and poly[r(T) X d(A) X r(T)], the least A-like.
mesh_terms: D000225:Adenine; D001482:Base Composition; D002942:Circular Dichroism; D004247:DNA; D009690:Nucleic Acid Conformation; D011119:Polynucleotides; D012313:RNA; D013329:Structure-Activity Relationship; D013941:Thymine; D014498:Uracil
chemical_list: D011119:Polynucleotides; C051802:triplex DNA; D014498:Uracil; D012313:RNA; D004247:DNA; D000225:Adenine; D013941:Thymine