Structural variants of double-stranded DNA: Z form

The Z form is a sinistrorse (left-handed) double helix, which makes it different from the A and B forms, and it is thinner. Note how the backbone (fictitious line joining the phosphorus atoms) progresses turning left and in addition makes a zig-zag line. This feature gives the Z form its name.

Spacefilling model, made of (bases and backbone).
What was the major groove in B-DNA becomes in the Z fom a shallow groove, while the minor groove is here narrow and deep.