DNA structure from A to Z.

Publisher Summary This chapter shows sixteen-base-pair lengths of A-, B-, and Z-DNA on a uniform scale, as a comparison and an illustration of their distinguishing features. Mean helix parameters for A-, B-, and Z-DNA as observed in single-crystal structure analyses of oligonucleotides are compared in the chapter. The A helix appears to be broader and more compressed along its axis relative to B and Z. A critical distinction is the displacement of base pairs from the helix axis. In B-DNA, the base pairs sit directly on the axis so that the major and minor grooves are of equal depth. In A DNA, the pairs are displaced off-axis in a direction that makes the major groove cavernously deep, and the minor groove extremely shallow. In Z-DNA, the base pairs are displaced in the opposite direction, yielding a deep minor groove and a major groove that is little more than a shallow depression winding around the helix cylinder.