Conformational studies of d(CACGTG)₂ and d(CACCGTG).d(CACGGTG) by two-dimensional 1h, 31p NMR and circular dichroism spectra

Abstract

The conformational studies of synthetic oligonucleotides d(CACGTG)₂ and d(CACCGTG).d(CACGGTG) by two-dimensional ₁H NMR (COSY and NOESY), ₃₁P NMR and CD spectroscopic methods are reported. The results suggest that these DMA duplexes adopt B-form globally and significant microheterogeneity persists in local conformation. In particular, the sugars of nucleotides C3 of the hexamer and C3, C10 of the heptamer exhibit 3'-endo conformations. These sequences fail to undergo B-Z transition in solution though, d(CACGTG)₂ is reported to crystallise in a left handed form. The conformational studies of titled DNA sequences by 2D ^p1H NMR (COSY and NOESY), ^p31p NMR and CD methods are reported. These duplexes adopt B-form with significant conformational heterogeneity at C3 of hexamer and C3, C10 of heptamer. They fail to exhibit B to Z transition in solution, though d(CACGTG)_f2 is reported to crystallise in a left hand form.