Z-DNA      [our left handed world]
   A Z-DNA configuration of DNA is the left-handed version of the WC model. The major and minor grooves do show a little difference in width and every other base in a Z-DNA stretch has a different orientation relative o the sugar-P backbone resulting in Z-DNA having a Zig-Zag shape. Z-DNA exists transiently in short stretches of up to 100 base pairs. The site where the DNA molecule switches chirality is known as the B-Z junction. At this point in the DNA polymer, on A-T pair projects to the outside of the double helix.
   Using protein antibodies to Z-DNA, P. Shing Ho found some 800 Z-DNA sequences across the Human genome, that seem to be clustered near the start of many eukaryotic genes. Z-DNA does not seem to occur within protein coding gene sequences.
     A. Herbert (1995) discovered a protein domain Za in a Z-DNA binding protein (ADARI) which binds to the backbone of this left handed DNA.  The ADARI-Za domain binds to double stranded RNA and converts Adenine to Inosine, that is read as Guanosine and involved in double strand RNA formation.
     Herbert's group (2019) studied mutations in the ADARI protein in the Za domain regions that were associated with a number of inherited inflammatory immune diseases, as Z-DNA is linked to the interferon production.