The A-DNA is favoured in many solutions that are relatively of water. The properties of A-DNA are:
1) Right-handed helix
2) Helix rise per base pair is 0.23 nm
3) The number of base pairs per helical turn is 11.
4) A-form DNA is shorter and has a greater helical diameter than the B-DNA. The helical diameter of A-DNA is 23 angstrom or 26 angstrom.
5) The rotation per base pair is 34.7°.
6) RNA-DNA and RNA-RNA helices also exist in this form.
7) The A-form is probably very close to the conformation of double stranded regions of RNA, where the presence of the 2′-OH group prevents the adoption of the B-form.
The major groove of A-DNA is less accessible and bases are tilted with regard to the helical axis. The A-DNA is sometimes formed during DNA crystallization because the reagents used to promote DNA crystallization tend to dehydrate it. This leads to a tendency for many DNAs to crystallize in the A-form.