Some rules for predicting the base-sequence dependence of DNA conformation.

Two tables have been constructed showing the crystal and solution conformations of short sequences of DNA. Each of these DNAs has been found to be in one of three different conformations--the A, B, or Z form--depending upon the base sequence and the environmental conditions. A set of rules is presented showing the tendency of certain base pairs to direct the DNA conformation into the A, B, or Z genus in saturated salt solutions and in crystals. These rules are based on a consideration of nearest-neighbor interactions that are interpreted in terms of 10 different two-letter code words made from the letters denoting the bases guanine (G), cytosine (C), adenine (A), and thymine (T). One table discusses the effect on DNA conformation of 3 strong words that tend to direct a DNA oligomer into either the A, B, or Z genus in crystals or in aqueous solutions containing a high salt concentration (6 M). The second table discusses the remaining 7 code words that appear to have a much weaker effect on conformation. The sequences that are most likely to lead to A-Z, B-Z, and A-B junctions are discussed, as is the possible biological significance of these rules.