title: Parallel and antiparallel G*G.C base triplets in pur*pur.pyr triple helices formed with (GA) third strands.
abstract: Triple helices with G*G.C and A*A.T base triplets with third GA strands either parallel or antiparallel with respect to the homologous duplex strand have been formed in presence of Na (+) or Mg(2+) counterions. Antiparallel triplexes are more stable and can be obtained even in presence of only monovalent Na(+) counterions. A biphasic melting has been observed, reflecting third strand separation around 20 degrees C followed by the duplex -> coil transition around 63 degrees C. Parallel triplexes are far less stable than the antiparallel ones. Their formation requires divalent ions and is observed at low temperature and in high concentration conditions. Different FTIR signatures of G*G.C triplets in parallel and antiparallel triple helices with GA rich third strands have been obtained allowing the identification of such base triplets in triplexes formed by nucleic acids with heterogeneous compositions. Only S-type sugars are found in the antiparallel triplex while some N-type sugar conformation is detected in the parallel triplex.
authors.affiliation: Laboratoire de Spectroscopie Biomoléculaire, UFR de Médecine, Université Paris 13, 74 rue Marcel Cachin, F93017 Bobigny Cedex, France.
authors.forename: J
authors.initials: J
authors.lastname: Liquier
authors.forename: F
authors.initials: F
authors.lastname: Geinguenaud
authors.forename: T
authors.initials: T
authors.lastname: Huynh-Dinh
authors.forename: C
authors.initials: C
authors.lastname: Gouyette
authors.forename: E
authors.initials: E
authors.lastname: Khomyakova
authors.forename: E
authors.initials: E
authors.lastname: Taillandier
mesh_terms: D000225:Adenine / Q000737:chemistry; D001483:Base Sequence; D002236:Carbohydrate Conformation; D002413:Cations, Divalent; D003596:Cytosine / Q000737:chemistry; D004247:DNA / Q000737:chemistry*; D006147:Guanine / Q000737:chemistry; D008274:Magnesium / Q000737:chemistry; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D009841:Oligonucleotides / Q000737:chemistry; D011687:Purines / Q000737:chemistry*; D011743:Pyrimidines / Q000737:chemistry*; D012964:Sodium / Q000737:chemistry; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013696:Temperature; D018911:Trinucleotide Repeats
chemical_list: D002413:Cations, Divalent; D009841:Oligonucleotides; D011687:Purines; D011743:Pyrimidines; C051802:triplex DNA; D006147:Guanine; D003596:Cytosine; D004247:DNA; D012964:Sodium; D008274:Magnesium; D000225:Adenine