Open AccessProtonated Polynucleotide Structures
Author(s) -
Courtois Y.,
Fromageot P.,
Guschlbauer W.
Publication year - 1968
Publication title -
european journal of biochemistry
Language(s) - English
Resource type - Journals
eISSN - 1432-1033
pISSN - 0014-2956
DOI - 10.1111/j.1432-1033.1968.tb00472.x
Subject(s) - polynucleotide , guanine , chemistry , crystallography , optical rotatory dispersion , cytosine , protonation , base pair , antiparallel (mathematics) , stereochemistry , thymine , guanosine , nucleobase , dna , pairing , nucleotide , circular dichroism , biochemistry , physics , ion , magnetic field , gene , superconductivity , organic chemistry , quantum mechanics
1 The change of the optical rotatory dispersion spectra as a function of pH of DNAs of different base composition and the synthetic polynucleotides poly d(A–T) and poly (dG) · poly (dC) has been studied. 2 It is shown that the acid titration of DNA when followed by optical rotatory dispersion is considerably more complex than it appears from ultraviolet absorption data. The gradual appearance of a peak at 260–270 mμ between pH 3 and 4 before acid denaturation, indicates a change of conformation of the guanosine residues in this pH region. 3 DNA methylated in N‐7 of guanine does not show this inversion of Cotton effects. It is concluded that this position plays an important role in the acid titration of DNA. 4 Protonation on N‐7 of guanine, rotation of guanine out of the helix, reversion into the syn ‐position, pairing in Hoogsteen manner and thus sharing the proton with N‐1 on cytosine is suggested as a possible interpretation of these results. 5 From the data presented it is concluded that poly (dG) · poly (dC) has a conformation and/or structure different from that of DNA (B‐form). In analogy with published data on nucleo‐sides, it is suggested that guanosine is in the syn ‐conformation. Three possible structures seem to be feasible: (a) Watson‐Crick pairing with parallel strands; (b) Hoogsteen pairing with anti‐parallel strands; (c) Watson‐Crick pairing with antiparallel strands in a left handed helix.