User:DubOOIan/sandbox2
From Wikipedia, the free encyclopedia
Triple-stranded DNA is a DNA structure in which three oligonucleotides wind around each other and form a triple helix.
There are two classes of triplex DNA: intermolecular and intramolecular formations. Intermolecular triplex refers to triplex formation between a duplex and a different strand of DNA. The third strand can either be from a neighboring chromosome or a triplex forming oligonucleotide (TFO). Intramolecular triplex DNA is formed from a duplex with homopurine and homopyrimidine strands with mirror repeat symmetry.[1] The level of supercoiling in DNA influences the level of intramolecular triplex formation.[2] There are two different types of intramolecular triplex DNA: H-DNA and H*-DNA. Formation of H-DNA is stabilized under acidic conditions and in the presence of divalent cations such as Mg2+. In this conformation, the homopyrimidine strand in the duplex bends back to bind to the purine strand in a parallel fashion. The base triads used to stabilize this conformation are T-A-*T and C-G*C+. The cytosine in this base triad needs to be protonated in order to form this intramolecular triple helix, which is why this conformation is stabilized under acidic conditions.[3] H*-DNA has favorable formation conditions at neutral pH and in the presence of divalent cations.[4] This intramolecular conformation is formed from the binding of the homopurine and purine strand of the duplex in an antiparallel fashion. It is stabilized by T-A*A and C-G*G base triplets.[5][6]