The high salt form of poly(dG-dC)·poly(dG-dC) is left-handed Z-DNA: Raman spectra of crystals and solutions

Abstract

The laser-Raman spectra of crystalline d(CpGpCpGpCpG) and of aqueous poly(dG-dC).poly(dG-dC) in high salt (4M NaCl) and low salt (0.1M NaCl) solutions have been measured and compared. The spectra of the crystal and the high-salt solution show a striking congruence, which indicates clearly that the high-salt form of the aqueous polymer has the left-handed Z-DNA structure of the crystalline oligomer. These two spectra differ substantially from that of the low-salt form of the polymer, which has been found previously to have spectral characteristics of the B-form of DNA. The high salt spectrum shows a unique line due to guanine residues at 625 cm-1 which should be useful for qualitative and possibly quantitative assessment of the amount of Z-structure present in a sample of DNA.

Evidence for Hoogsteen GC Base Pairs in the Proton-Induced Transition from Right-Handed to Left-Handed Poly(dG-dC)·Poly(dG-dC)

“…Changes in the cytosine bands between 1200 and 1280 cm -1 are also apparent. All these changes are in agreement with earlier Raman spectroscopic investigations of the B-and Z-form DNAs (Thamann et al, 1981;Benevides & Thomas, 1983).…”

“…In a high-salt environment, it was established, by means of CD and Raman spectra, that the polynucleotide has a left-handed double-helical structure (Pohl & Jovin, 1972;Thamann et al, 1981;Benevides & Thomas, 1983).…”

Interaction of Z form poly(dG-dC). poly(dG-dC) with divalent metal ions: localization of the binding sites by I.R. spectroscopy

“…circular dichroism experiments (1), has been confirmed by X ray crystal diffraction studies (2,3) and characterized by other various techniques: 31P and 1H NMR (4-7), Raman (8,9) and IR spectroscopy (9,10). In native systems, the existence of such conformations has been evidenced by indirect immunological techniques (12)(13)(14).…”

Structure of d(CACGCG)\cdotd(CGCGTG) in Crystals Grown in the Presence of RutheniumIIIHexammine Chloride

“…Crystals of several different sequences grown in a variety of conditions assume almost identical left-handed double-helical structures (Ho & Mooers, 1997). It has been shown that even the absence of high salt, earlier thought to be necessary (Pohl & Jovin, 1972;Thaman et al, 1981;Thomas & Peticolas, 1984), could be compensated by other factors such as methylation of cytosine (Behe & Felsenfeld, 1981;Malfoy et al, 1982;Jovin et al, 1983;Wang et al, 1985). Hexammine salts are helix-stabilizing agents (Ascoli et al, 1973;Eichorn, 1982;Hingerty et al, 1982).…”