Base-Modified 2′-Deoxyribonucleosides in Bended DNA Fragments: Differential Bending at 3′- and 5′- Junctions of H- and B-DNA

Abstract

DNA-Sequences containing repeated (dA)_n·(dT)_n tracts in phase with B-DNA helical repeat show strongly decreased mobility in polyacrylamide g a electrophoresis. This phenomenon is the result of intrinsic, sequence-directed bending of DNA and was first observed by Marini et al. [1]. As the d(GGCA₆C). d(GT₆GCC) duplex contains a tract of 6 dA residues it is bended. We have oligomerized duplexes containing 2′-deoxytubercidin (c⁷A_d,1a) instead of dA at various positions of the d(A)₆ tract with DNA-ligase. This replacement should allow the correlation of DNA-bending with stacking mteractions of the nucleobase.