title: The HIV-1(Lai) RNA dimerization. Thermodynamic parameters associated with the transition from the kissing complex to the extended dimer.
abstract: Retroviruses contain dimeric RNA consisting of two identical copies of the genomic RNA. The interaction between these two RNA molecules occurs near their 5' ends. A region upstream from the splice donor comprising an auto-complementary sequence has been identified as being responsible for the initiation of the formation of dimeric HIV-1(Lai) RNA. This region (SL1), part of the PSI encapsidation domain, can adopt a stem-loop structure. It has already been shown that this stem-loop structure can initiate the formation of two distinct dimers differing in their thermostability: a loop-loop dimer or 'kissing complex' and an extended dimer. We report here a study using UV and 1D NMR spectroscopy of the dimerization of a short oligoribonucleotide (23 nucleotides) spanning nucleotides 248-270 of the HIV-1(Lai) SL1 sequence, in order to derive the thermodynamic parameters associated with the transition from the loop-loop complex to the extended dimer. The temperature dependence of the UV absorbency shows an hypochromicity for this transition with a small enthalpy change equal to - 29.4 +/- 5 kcal x mol-1, together with a concentration independent transition which implies a monomolecular reaction. On the other hand, our NMR results don't indicate a dissociation of the GCGCGC sequence engaged in the loop-loop interaction during the rearrangement of the loop-loop complex into the extended dimer. Our data suggest that the loop-loop interaction is maintained during the temperature dependent conformational change while the intramolecular base-pairing of the stems is disrupted and then reconstituted to form an intermolecular base-pairing leading to an extended dimer.
authors.affiliation: Centre de Biophysique Moléculaire, UPR 4301 CNRS conventionnée avec l'Université d'Orléans, Orléans, France.
authors.forename: V
authors.initials: V
authors.lastname: Theilleux-Delalande
authors.forename: F
authors.initials: F
authors.lastname: Girard
authors.forename: T
authors.initials: T
authors.lastname: Huynh-Dinh
authors.forename: G
authors.initials: G
authors.lastname: Lancelot
authors.forename: J
authors.initials: J
authors.lastname: Paoletti
mesh_terms: D001483:Base Sequence; D017931:DNA Primers; D019281:Dimerization; D015497:HIV-1 / Q000235:genetics*; D009682:Magnetic Resonance Spectroscopy; D009690:Nucleic Acid Conformation; D012367:RNA, Viral / Q000737:chemistry* / Q000235:genetics; D013056:Spectrophotometry, Ultraviolet; D013816:Thermodynamics
chemical_list: D017931:DNA Primers; D012367:RNA, Viral