title: DNA triplex formation of oligonucleotide analogues consisting of linker groups and octamer segments that have opposite sugar-phosphate backbone polarities.
abstract: The DNA oligomer analogues 3'd(CTTTCTTT)5'-P4-5'd(TTCTTCTT)3' (IV), 5'd-(TTTCTTTC)3'-P2-3'd(CTTTCTTT)5' (V), and 5'd(TTTCTTTC)3'-P2-3'd(CTTTCTTT)5'-P4-5'd-(TTCTTCTT)3' (VI) (P2 = P*P and P4 = P*P*P*P, where P = phosphate and * = 1,3-propanediol) have been synthesized. These oligomers consist of a linker group or groups and homopyrimidine oligonucleotides which have opposite sugar-phosphate backbone polarities. These oligomer analogues are designed to form triplexes with a duplex, 5'd(AAAGAAAGCCCTTTCTTTAAGAAGAA)3'.5'd(TTCTTCTTAAA- GAAAGGGCTTTCTTT)3' (I), which contains small homopurine clusters alternately located in both strands. The length of the linker groups, P2 and P4, was based upon a computer modeling analysis. Triplex formation by the unlinked octamers 5'd(TTCTTCTT)3' (II) and 5'd(TTTCTTTC)3' (III) and the linked oligomer analogues IV-VI with the target duplex was studied by thermal denaturation at pH 5.2. The order of stabilities of triplex formation by these oligomers was I-V much much greater than I-IV greater than I-(II, III). The mixture of I and VI showed two transitions corresponding to the dissociation of the third strand. The higher transition corresponded to the dissociation of 3'-3'-linked octamer segments, and the lower one corresponded to the dissociation of 5'-5'-linked octamer segments. The Tm of the latter transition was higher than that of the I-IV triplex; thus the triplex formed by the 5'-5'-linked octamer segment was stabilized by the triplex formed by the 3'-3'-linked octamer segments in the I-VI triplex. Triplex formation of this system was also studied in the presence of ethidium bromide.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Department of Biochemistry, School of Hygiene and Public Health, Johns Hopkins University, Baltimore, Maryland 21205.
authors.forename: A
authors.initials: A
authors.lastname: Ono
authors.forename: C N
authors.initials: CN
authors.lastname: Chen
authors.forename: L S
authors.initials: LS
authors.lastname: Kan
mesh_terms: D001483:Base Sequence; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D015226:Dinucleoside Phosphates / Q000138:chemical synthesis / Q000737:chemistry*; D006358:Hot Temperature; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009841:Oligonucleotides / Q000138:chemical synthesis* / Q000737:chemistry
chemical_list: D015226:Dinucleoside Phosphates; D009841:Oligonucleotides; D004247:DNA