The Z-DNA is a left handed helical form of DNA. With the Z-DNA the double helix twists to the left in a zig zag pattern, instead of twisting to the right like the more common B-DNA.
Z-DNA was the first crystal structure of a DNA molecule that has been managed to be solved by scientists. This event happened in 1979 thanks to Alexander Rich and his co workers at MIT.
The Z-DNA is very different from the more common right handed forms of DNA. These different qualities are actually usually highlighted in the comparisons with the B-DNA in order to further present their intrinsic differences. Z-DNA is actually a unique type of DNA that is formed under sequence dependent conditions. These conditions would require a purine – pyrimidine sequence. There are other factors involving chemical and environmental elements that are conducive to the formation of Z-DNA. Among these are high salt environments, the presence of soma cations, and DNA supercoiling.
At present there are still no very definite biological significance that is being associated with the presence of Z-DNA. But it is commonly believed that it gives a torsional strain relief while DNA transcription is happening.
Web Resources On ZDNA
Z-DNA, the Bad DNA
Z-DNA-forming sequences generate large-scale deletions in mammalian cells
Book Resources On ZDNA
An A to Z of DNA Science: What Scientists Mean When They Talk About Genes and Genomes by Witherly et al.
From Genes to Genomes: Concepts and Applications of DNA Technology by Dale & von Schantz