Final answer:
Negative supercoiling increases the chance of cruciform formation in DNA. This occurs when DNA is under-wound, allowing for special structures to form in palindromic sequence areas, which is important for DNA packaging and regulation within cells.
Step-by-step explanation:
The kind of supercoiling that increases the chance of cruciform formation is negative supercoiling. Negative supercoiling is when the DNA is under-wound, having less than one turn of the helix per 10 base pairs. This under-wound state introduces tension that can facilitate the formation of secondary structures such as cruciforms, especially in areas where the DNA sequence is palindromic, allowing for intra-chain base pairing. Enzymes like DNA gyrase, as well as changes in conditions like salt concentrations, can affect the state of DNA supercoiling and thus affect the formation of such structures.
Supercoiling plays a crucial role in DNA packaging and regulation. In prokaryotes like E. coli, the entire genome needs to fit within a small cellular space, which is facilitated by supercoiling. In eukaryotes, DNA is packaged around histones to form nucleosomes, and further supercoiling helps in compacting the DNA within the cell nucleus.