title: Triplexes with 8-Aza-2'-deoxyisoguanosine replacing protonated dC: probing third strand stability with a fluorescent nucleobase targeting duplex DNA.
abstract: The fluorescent 8-aza-2'-deoxyisoguanosine (4) as well as the parent 2'-deoxyisoguanosine (1) were used as protonated dCH(+) surrogates in the third strand of oligonucleotide triplexes. Stable triplexes were formed by Hoogsteen base pairing. In contrast to dC, triplexes containing nucleoside 1 or 4 in place of dCH(+) are already formed under neutral conditions or even at alkaline pH values. Triplex melting can be monitored separately from duplex dissociation in cases in which the third strand contains the fluorescent nucleoside 4. Third-strand binding of oligonucleotides with 4, opposite to dG, was selective as demonstrated by hybridisation experiments studying mismatch discrimination. Third-strand binding is more efficient when the stability of the DNA duplex is reduced by mismatches, giving third-strand binding more flexibility.
authors.affiliation: Laboratory of Bioorganic Chemistry and Chemical Biology, Center for Nanotechnology, Heisenbergstrasse 11, 48149 Münster Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Seela
authors.forename: Dawei
authors.initials: D
authors.lastname: Jiang
authors.forename: Simone
authors.initials: S
authors.lastname: Budow
mesh_terms: D020137:Base Pair Mismatch; D004247:DNA / Q000737:chemistry*; D003845:Deoxycytosine Nucleotides / Q000737:chemistry*; D003849:Deoxyguanosine / Q000031:analogs & derivatives* / Q000737:chemistry; D005456:Fluorescent Dyes / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature
chemical_list: C552849:8-aza-2'-deoxyisoguanosine; D003845:Deoxycytosine Nucleotides; D005456:Fluorescent Dyes; C051802:triplex DNA; D004247:DNA; D003849:Deoxyguanosine