Intramolecular folding of a fragment of the cytosine-rich strand of telomeric DNA into an i-motif.
In the recently discovered i-motif, four stretches of cytosine form two parallel-stranded duplexes whose C.C+ base pairs are fully intercalated. The i-motif may be recognized by characteristic Overhauser cross-peaks of the proton NMR spectrum, reflecting short H1'-H1' distances across the minor groove, and short internucleotide amino-proton-H2'/H2" across the major groove. We report the observation of such cross-peaks in the spectra of a fragment of the C-rich telomeric strand of vertebrates, d[CCCTAA]3CCC. The spectra also demonstrate that the cytosines are base-paired and that proton exchange is very slow, as reported previously for the i-motif. From UV absorbance and gel chromatography measurements, we assign these properties to an i-motif which includes all or nearly all the cytosines, and which is formed by intramolecular folding at slightly acid or neutral pH. A fragment of telomeric DNA of Tetrahymena, d[CCCCAA]3CCCC, has the same properties. Hence four consecutive C stretches of a C-rich telomeric strand can fold into an i-motif. Hypothetically, this could occur in vivo.
Leroy
J L
JL
l'URA D1254 du CNRS, Palaiseau, France.
Guéron
M
M
Mergny
J L
JL
Hélène
C
C
D000818:Animals; D001482:Base Composition; D001483:Base Sequence; D002850:Chromatography, Gel; D003596:Cytosine / Q000737:chemistry*; D004247:DNA / Q000737:chemistry*; D016054:DNA, Protozoan / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D011522:Protons; D013056:Spectrophotometry, Ultraviolet; D016615:Telomere / Q000737:chemistry*; D013768:Tetrahymena / Q000235:genetics*
D016054:DNA, Protozoan; D011522:Protons; D003596:Cytosine; D004247:DNA