Hoogsteen bonds

The central strand of the triplex must be purine rich since a pyrimidine does not have two hydrogen bonding surfaces with more than one hydrogen bond. Thus triple-stranded DNA requires a homopurine homopyrimidine region of DNA. If the third strand is purine rich, it forms reverse Hoogsteen hydrogen bonds in an antiparallel orientation with the purine strand of the Watson-Crick helix. If the third strand is pyrimidine rich, it forms Hoogsteen bonds in a parallel orientation with the Watson-Crick paired purine strand. 

Linak et al. developed a 3-site per nucleotide CG model that includes non-WC bonds, relying on a top-down approach, to study the hybridization of ssDNA and dsDNA hairpins (Linak et al., 2011). Their model explicitly takes into account the formation of Hoogsteen bonds, which are known to stabilize multi-body secondary structures in DNA. The model reproduces many of the microscopic features of dsDNA and captures the experimental melting curves for a number of short DNA hairpins. 

Three classes of nucleic acid triple helices have been described for oligonucleotides containing only natural units. They differ according to the base sequences and the relative orientation of the phosphate-deoxyribose backbone of the third strand. All the three classes involve Hoogsteen or reverse Hoogsteen-like hydrogen bonding interaction between the triple helix form-... 

Hoogsteen hydrogen bonding, 17 609, 610 Hooke s law, 21 719 Hookean region of stress—strain curve, 11 183, 184... 

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