The HIV-1(Lai) RNA dimerization. Thermodynamic parameters associated with the transition from the kissing complex to the extended dimer

• Published in: European journal of biochemistry Vol. 267; no. 9; pp. 2711 - 2719
• Main Authors: Theilleux-Delalande, V, Girard, F, Huynh-Dinh, T, Lancelot, G, Paoletti, J
• Format: Journal Article
• Language: English
• Published: England 01-05-2000
• Subjects: AIDS/HIV; Base Sequence; Dimerization; DNA Primers; HIV-1 - genetics; Magnetic Resonance Spectroscopy; Nucleic Acid Conformation; RNA, Viral - chemistry; RNA, Viral - genetics; Spectrophotometry, Ultraviolet; Thermodynamics
• ISSN: 0014-2956
• DOI: 10.1046/j.1432-1327.2000.01292.x

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.