Today I would be writing about a very unusual form of DNA, that is, H-DNA.
The H-DNA is a triple helix. This particularly unusual form of DNA is found in vitro or possibly during recombination and DNA repair. It forms by pairing and interwinding of 3 strands of DNA. Two of the three strands contain pyrimidines and the third contains purines. The three strands show a special base pairing known as Hoogsteen base pairing. Some sequences that can form H-DNA are found within regions involved in the regulation of a number of genes in eukaryotes.
You can read the following article about the H-DNA: