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Virology. 2007 Mar 1;359(1):105-15. Epub 2006 Oct 19.

A second-site suppressor significantly improves the defective phenotype imposed by mutation of an aromatic residue in the N-terminal domain of the HIV-1 capsid protein.

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  • 1Viral Gene Regulation Section, Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Building 6B, Room 216, Bethesda, MD 20892-2780, USA.


The HIV-1 capsid (CA) protein plays an important role in virus assembly and infectivity. Previously, we showed that Ala substitutions in the N-terminal residues Trp23 and Phe40 cause a severely defective phenotype. In searching for mutations at these positions that result in a non-lethal phenotype, we identified one candidate, W23F. Mutant virions contained aberrant cores, but unlike W23A, also displayed some infectivity in a single-round replication assay and delayed replication kinetics in MT-4 cells. Following long-term passage in MT-4 cells, two second-site mutations were isolated. In particular, the W23F/V26I mutation partially restored the wild-type phenotype, including production of particles with conical cores and wild-type replication kinetics in MT-4 cells. A structural model is proposed to explain the suppressor phenotype. These findings describe a novel occurrence, namely suppression of a mutation in a hydrophobic residue that is critical for maintaining the structural integrity of CA and proper core assembly.

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