Cruciform DNA

Cruciform DNA is a secondary structure on a helical double-stranded DNA molecule that comprises a four-way junction and two closed hairpin-shaped points. Double-stranded inverted repeats or DNA palindromes have the potential to form cruciform structures by intrastrand base pairing to extrude a pair of stem-loop structures under conditions of negative superhelicity. The junction of the cruciform is equivalent to a Holliday junction, which is a homologous recombination intermediate that is crucial for the maintenance of genomic integrity. Hence, cruciform DNA structures are recognized by several structure-specific enzymes, such as Holliday junction resolvases. Although cruciform formation in vivo remains to be validated, it is speculated that the formation of these unusual structures may fulfill a vital biological role or possibly induce genomic instabilities leading to deletions or chromosomal translocations.