Experimental support for a right‐handed vertical double helix

Abstract

SynopsisThe experimentally observed geometry of a miniature double helix of high anti (XCN The theoretically computed chemical shift changes for the various double-helical configurations show that for the system examined, only the vertical model can explain the experimentally observed shift trends. The melting curve for the helix-coil transition for high anti dinucleoside monophosphate has been observed for the first time. Even though the experimental data support vertical double helices when XCN is fixed a t 120", data on naturally occurring nucleic acid structures indicate that they have no proclivity to enter into vertically stabilized double-helical arrays. THE PROBLEMIt is known that in aqueous solution the magnitude of the glycosyl torsion angle (x) has a decisive effect on the mode of sugar pucker and the C4'-C5' (#) t o r~i o n l -~ in nucleic acid structures. It has further been shown6 experimentally that when x is fixed at a high anti domain ( N 120°), the sense of the base stack is left-handed. However, the effect of a high anti arrangement on the helical organization of the backbone of a polynucleotide is not known with any certainty, and two diametrically opposed views have been reported about its helix handedness. OPPOSING MODELSThe observation that the Cotton effect in the spectra of high anti polynucleotides was opposite to that of normal nucleic acid counterpart^^^^ suggested the possibility that their helical organization may be left-handed. Fujii and Tomitag carried out conformational energy calculations and

Hybrid Oligomer of Cyclonucleotides and Deoxynucleotides. A High Anti Left-handed Double Helical DNA Structure

“…These phenomena are reflection of difference in the modes of stacking in left-handed and right-handed stacks. A'pU 0 , but not U 0 pA', forms a left-handed self-duplex (13,14). Energy calculation on NpN conformation also supports that the left-handed stack is the most stable one (15).…”

Principles of Nucleic Acid Structure

“…The proposal of the "vertical" double helix was based entirely on computerized model building studies but has found support from spectroscopic studies on homopolynucleotides fixed in the high-anti (-sc) conformation which are able to form single-, double-, and triple-helical structures reminiscent of the poly(A) . poly(U) system (1024)(1025)(1026).…”

Left-handed deoxyribonucleic acid double helix in solution

“…It is important to point out that the detailed computations of the magnetic shielding constants presented in this paper are based on the NMR theory for nucleic acids developed by Pullman and Giessner-Prettre over the period of the last decade; the several references cited in this paper from their laboratory are only a small part of this monumental work. In the past, this NMR theory has been successfully employed to derive the solution conformations of single-stranded oligo-nucleotides and miniature double helices (Cheng et al, 1980;Mitra et al, 1980a;Sarma et al, 1979). The present paper represents their successful application to larger systems.…”