STUDIES ON NUCLEIC ACID STRUCTURE AND METAL ION - NUCLEIC ACID INTERACTIONS USING RAMAN SPECTROSCOPY
Abstract
The structure of calf thymus DNA reacted with H('+), CH(,3)Hg(NO(,3)), cis-{PtCl(,2)(NH(,3))(,2)} (cis-DDP), and trans-{PtCl(,2)(NH(,3))(,2)} (trans-DDP) is studied. The Raman difference spectra of cis- and trans-DDP interacting with polyuridylic acid and polycytidylic acid is also reported. Additionally, the structure of the triple-stranded helix, poly(U)(.)poly(A)(.)poly(U) is probed using Raman difference spectroscopy. The binding of protons to adenine and cytosine residues is accompanied by a decrease in the percentage of DNA in the B conformation and a concurrent increase in a conformation most probably related to the C form. The denaturation of DNA is observed at a pH of 3.3 and parallels the protonation of guanine bases. The Raman spectra of calf thymus DNA in the basic region (above pH 10) show that guanine residues are deprotonated at a lower pH value than thymine residues. The reaction of calf thymus DNA with CH(,3)Hg(II) shows an order of binding as G (GREATERTHEQ) T > C > A. The electrophilic attack of cis- and trans-DDP on calf thymus DNA, however, produce different orders of binding: cis-DDP - G > C ('(TURN)) A >> T, trans-DDP - G ('(TURN)) C ('(TURN)) A >> T. The reaction of CH(,3)Hg(II) with DNA results in a decrease in the percentage of B form DNA, whereas the reactions of cis- and trans-DDP with DNA decrease the percentage of B DNA and cause the formation of C DNA structure. Binding of cis-DDP to polyuridylic acid results in the formation of a "platinum blue" species above r(,t) = 0.20. The interactions of cis- and trans-DDP with polycytidylic acid are bifunctional. The structure of the ribose-phosphate backbone, the base stacking, and the base pairing of triple helical poly(U)(.)poly(A)(.)poly(U) is investigated. In triple stranded poly(U)(.)poly(A)(.)poly(U) the first poly(U) strand is paired with poly(A) in Watson-Crick base pairing: the backbone conformation of that unit is A form (C3'-endo ribose). The second poly(U) chain, however, appears to exist in a C-type conformation (C2'-endo).
Degree
Ph.D.
Subject Area
Biophysics
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