Transmission electron microscopy reveals an optimal HIV-1 nucleocapsid aggregation with single-stranded nucleic acids and the mature HIV-1 nucleocapsid protein.
HIV-1 nucleocapsid protein (NCp7) condenses the viral RNA within the mature capsid. In a capsid-free system, NCp7 promotes an efficient mechanism of aggregation with both RNA and DNA. Here, we show an analysis of these macromolecular complexes by dark-field imaging using transmission electron microscopy. Thousands of mature NCp7 proteins co-aggregate with hundreds of single-stranded circular DNA molecules (ssDNA) within minutes, as observed with poly(rA). These co-aggregates are highly stable but dynamic structures, as they dissociate under harsh conditions, and after addition of potent ssDNA or NCp7 competitive ligands. The N-terminal domain and zinc fingers of NCp7 are both required for efficient association. Addition of magnesium slightly increases the avidity of NCp7 for ssDNA, while it strongly inhibits co-aggregation with relaxed circular double-stranded DNA (dsDNA). This DNA selectivity is restricted to mature NCp7, compared to its precursors NCp15 and NCp9. Moreover, for NCp15, the linkage of NCp7 with the Gag C-terminal p6-peptide provokes a deficiency in ssDNA aggregation, but results in DNA spreading similar to prototypical SSB proteins. Finally, this co-aggregation is discussed in a dynamic architectural context with regard to the mature HIV-1 nucleocapsid. On the basis of the present data, we propose that condensation of encapsidated RNA requires the C-terminal processing of NCp. Subsequently, disassembly of the nucleocapsid should be favoured once dsDNA is produced by HIV-1 reverse transcriptase.
Mirambeau
Gilles
G
Laboratoire de Microscopie Moléculaire et Cellulaire, CNRS UMR 8126, Institut Gustave Roussy, 94805 Villejuif, France. gilles.mirambeau@free.fr
Lyonnais
Sébastien
S
Coulaud
Dominique
D
Hameau
Laurence
L
Lafosse
Sophie
S
Jeusset
Josette
J
Justome
Anthony
A
Delain
Etienne
E
Gorelick
Robert J
RJ
Le Cam
Eric
E
D036022:Capsid Proteins / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D004247:DNA / Q000737:chemistry* / Q000648:ultrastructure; D004277:DNA, Single-Stranded / Q000737:chemistry* / Q000648:ultrastructure; D015683:Gene Products, gag / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D015497:HIV-1 / Q000378:metabolism; D008274:Magnesium / Q000737:chemistry*; D046529:Microscopy, Electron, Transmission; D019590:Nucleocapsid Proteins / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D017434:Protein Structure, Tertiary; D014764:Viral Proteins / Q000737:chemistry* / Q000235:genetics / Q000648:ultrastructure; D054301:gag Gene Products, Human Immunodeficiency Virus
D036022:Capsid Proteins; D004277:DNA, Single-Stranded; D015683:Gene Products, gag; C071884:NCP7 protein, Human immunodeficiency virus 1; D019590:Nucleocapsid Proteins; D014764:Viral Proteins; D054301:gag Gene Products, Human Immunodeficiency Virus; C060295:p15 gag protein, Human immunodeficiency virus 1; D004247:DNA; D008274:Magnesium