Using circular dichroism spectroscopy, UV absorption spectroscopy and polyacrylamide gel electrophoresis, we studied conformational properties of guanine-rich DNA strands of the fragile X chromosome repeats d(GGC)n, d(GCG)n and d(CGG)n, with n = 2, 4, 8 and 16. These strands are generally considered in the literature to form guanine tetraplexes responsible for the repeat expansion. However, we show in this paper that the repeats are reluctant to form tetraplexes. At physiological concentrations of either Na+ or K+ ions, the hexamers and dodecamers associate to form homoduplexes and the longer repeats generate homoduplexes and hairpins. The tetraplexes are rarely observed being relatively most stable with d(GGC)n and least stable with d(GCG)n. The tetraplexes are exclusively formed in the presence of K+ ions, at salt concentrations higher than physiological, more easily at higher than physiological temperatures, and they arise with extremely long kinetics (even days). Moreover, the capability to form tetraplexes sharply diminishes with the oligonucleotide length. These facts make the concept of the tetraplex appearance in this motif in vivo very improbable. Rather, a hairpin of the fragile X repeats, whose stability increases with the repeat length, is the probable structure responsible for the repeat expansion in genomes.

• MeSH
• cirkulární dichroismus MeSH
• DNA chemie   účinky léků   genetika   metabolismus   MeSH
• elektroforéza v polyakrylamidovém gelu MeSH
• G-kvadruplexy MeSH
• guanin metabolismus   MeSH
• kinetika MeSH
• konformace nukleové kyseliny * účinky léků   MeSH
• lidé MeSH
• lidské chromozomy X genetika   MeSH
• oligodeoxyribonukleotidy chemie   genetika   metabolismus   MeSH
• osmolární koncentrace MeSH
• sekvence nukleotidů MeSH
• soli farmakologie   MeSH
• spektrofotometrie ultrafialová MeSH
• syndrom fragilního X genetika   MeSH
• termodynamika MeSH
• trinukleotidové repetice genetika   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA MeSH
• guanin MeSH
• oligodeoxyribonukleotidy MeSH
• soli MeSH

UV absorption and CD spectroscopy, along with polyacrylamide gel electrophoresis, were used to study conformational properties of DNA fragments containing the trinucleotide repeat (GCC)(n) (n = 4, 8 or 16), whose expansion is correlated with the fragile X chromosome syndrome. We have found that the conformational spectrum of the (GCC)(n) strand is wider than has been shown so far. (GCC)(n) strands adopt the hairpin described in the literature under a wide range of salt concentrations, but only at alkaline (>7.5) pH values. However, at neutral and slightly acid pH (GCC)(4) and (GCC)(8) strands homodimerize. Our data suggest that the homodimer is a bimolecular tetraplex formed by two parallel-oriented hairpins held together by hemi-protonated intermolecular C.C(+) pairs. The (GCC)(16) strand forms the same tetraplex intramolecularly. We further show that below pH 5 (GCC)(n) strands generate intercalated cytosine tetraplexes, whose molecularity depends on DNA strand length. They are tetramolecular with (GCC)(4), bimolecular with (GCC)(8) and monomolecular with (GCC)(16). i-Tetraplex formation is a complex and slow process. The neutral tetraplex, on the other hand, arises with fast kinetics under physiological conditions. Thus it is a conformational alternative of the (GCC)(n) strand duplex with a complementary (GGC)(n) strand.

• MeSH
• cirkulární dichroismus MeSH
• dimerizace MeSH
• DNA chemie   MeSH
• elektroforéza v polyakrylamidovém gelu MeSH
• konformace nukleové kyseliny * MeSH
• lidé MeSH
• spektrofotometrie ultrafialová MeSH
• syndrom fragilního X genetika   MeSH
• trinukleotidové repetice * MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• DNA MeSH