Heteronomous DNA

Abstract

A fibrous form of poly d(A):poly d(T) has a heteronomous secondary structure which is the first to be confirmed for a polynucleotide duplex: although both chains are 10(1) helices, mutually hydrogen-bonded in the standard (Watson-Crick) fashion, each has a quite different conformation. One chain -- probably poly d(A) -- has C3'-endo-puckered furanose rings characteristic of the A family of polynucleotide secondary structures while the other -- probably poly d(T) -- has the C2'-endo-puckered rings of the B family. Since analogous heteronomous structures could be assumed by DNA-DNA or DNA-RNA duplexes containing more general base sequences the polymorphic range of polynucleotide double-helices may be even greater than we have come to suppose.

The influence of exocyclic substituents of purine bases on DNA curvature.

“…The curvature is modulated by the type of substituent at position 6 of the purine base in the major groove and by the arrangement of the modified purines. In agreement with x-ray fiber diffraction data (36,37), these data indicate that adjacent base pairs in the dA"-dT,, blocks close toward the minor groove (33). This causes the direction of the wedge roll angle between the adjacent base pairs to be negative.…”

“…In both cases (34,35) the dA"*dTn tracts appear as a B'-form structure, which differs from B-DNA mainly in the tilt angle of the base pairs relative to the respective helix axis (35)(36)(37). If a DNA fragment contains stretches of the two different conformations, the base pairs at the junctions are assumed to show perfect base stacking.…”

A bifurcated hydrogen-bonded conformation in the d(A.T) base pairs of the DNA dodecamer d(CGCAAATTTGCG) and its complex with distamycin.

“…The model of Alexeev et al (18) has a high propeller twist but the distance between the N-6 of adenine and the 0-4 of the thymine (3.6 A) is too long for a bifurcated hydrogen bond. Our model is also quite different from the heteronomous proposal, which has different conformations in each chain (20).…”

Computer modelling of DNA structures involved in chromosome maintenance

“…The helix junction model (7) states that tracts of oligo(dA) longer than two nucleotides adopt an altered conformation related to the structure of poly(dA) (12).…”