title: Promotion of duplex and triplex DNA formation by polycation comb-type copolymers.
abstract: Triplex DNA has attracted considerable interest recently because of its possible biological functions in vivo and its wide variety of potential applications, such as regulation of gene expression, site-specific cleavage of duplex DNA, mapping of genomic DNA, and gene-targeted mutagenesis (1-3). A triplex is usually formed through the sequence-specific interaction of a single-stranded homopyrimidine or homopurine triplex-forming oligonucleotide (TFO) with the major groove of the homopurine-homopyrimidine stretch in duplex DNA (1-5). In the pyrimidine motif triplex, a homopyrimidine TFO binds parallel to the homopurine strand of the target duplex by Hoogsteen hydrogen bonding to form T[Symbol: see text]A:T and C(+[Symbol: see text])G:C triplets ([Symbol: see text] and : represent Hoogsteen hydrogen bonding and Watson Crick base pairing, respectively). (1-5). Because the cytosine bases in a homopyrimidine TFO are to be protonated to bind with the guanine bases of the G:C duplex, the formation of the pyrimidine motif triplex needs an acidic pH condition, and is thus unstable at physiological pH (6-8). On the other hand, in the purine motif triplex, a homopurine TFO binds antiparallel to the homopurine strand of the target duplex by reverse Hoogsteen hydrogen bonding to form A[Symbol: see text]A:T (or T[Symbol: see text]A:T) and G[Symbol: see text]G:C triplets (1-5). Although the purine motif triplex is pH-independent, triplexes involving guanine-rich TFOs are inhibited by physiological concentrations of certain monovalent cations (M(+)), especially K(+) (9,10).
authors.affiliation: Tsukuba Life Science Center, Institute of Physical and Chemical Research (RIKEN), Tsukuba, Ibaraki, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Torigoe
authors.forename: A
authors.initials: A
authors.lastname: Maruyama