Structure and stability of wild-type and mutant RNA internal loops from the SL-1 domain of the HIV-1 packaging signalGreatorex, J., Gallego, J., Varani, G., Lever, A.
(2002) J.Mol.Biol. 322: 543-557
- PubMed: 12225748
- PubMed Abstract:
The packaging signal (Psi) of the human immunodeficiency virus type 1 (HIV-1) enables encapsidation of the full-length genomic RNA against a background of a vast excess of cellular mRNAs. The core HIV-1 Psi is approximately 109 nucleotides and contai ...
The packaging signal (Psi) of the human immunodeficiency virus type 1 (HIV-1) enables encapsidation of the full-length genomic RNA against a background of a vast excess of cellular mRNAs. The core HIV-1 Psi is approximately 109 nucleotides and contains sequences critical for viral genomic dimerisation and splicing, in addition to the packaging signal. It consists of a series of stem-loops (termed SL-1 to SL-4), which can be arranged in a cloverleaf secondary structure. Using a combination of NMR spectroscopy, UV melting experiments, molecular modeling and phylogenetic analyses, we have explored the structure of two conserved internal loops proximal to the palindromic sequence of SL-1. Internal loop A, composed of six purines, forms a flexible structure that is strikingly similar to the Rev responsive element motif when bound to Rev protein. This result suggests that it may function as a protein-binding site. The absolutely conserved four-purine internal loop B is instead conformationally and thermodynamically unstable, and exhibits multiple conformations in solution. By introducing a double AGG to GGA mutation within this loop, its conformation is stabilised to form a new intra-molecular G:A:G base-triplet. The structure of the GGA mutant explains the relative instability of the wild-type loop. In a manner analogous to SL-3, we propose that conformational flexibility at this site may facilitate melting of the structure during Gag protein capture or genomic RNA dimerisation.
Department of Medicine, University of Cambridge, Level 5, Addenbrookes Hospital, Hills Road, CB2 2QQ, Cambridge, UK.