DNA bending at adenine · thymine tracts

Abstract
Intrinsic bending of DNA molecules results from local structural polymorphism in regions of homopolymeric dA · dT which are at least 4 base pairs long; the A · T tracts must be repeated in phase with the helix screw. Bending, in the direction of base-pair tilt rather than roll, occurs at the junctions between the A · T tract and adjacent B-DNA, with a larger angle at the 3′ than at the 5′ end of the A tract.