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Virology. 2009 Oct 25;393(2):286-94. doi: 10.1016/j.virol.2009.07.031. Epub 2009 Aug 29.

Ubiquitin-fusion as a strategy to modulate protein half-life: A3G antiviral activity revisited.

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URIA-Centro Patogénese Molecular, Faculdade de Farmácia da Universidade Lisboa, Lisboa 1649-059, Portugal.


The human APOBEC3G (A3G) is a potent inhibitor of HIV-1 replication and its activity is suppressed by HIV-1 virion infectivity factor (Vif). Vif neutralizes A3G mainly by inducing its degradation in the proteasome and blocking its incorporation into HIV-1 virions. Assessing the time needed for A3G incorporation into virions is, therefore, important to determine how quickly Vif must act to induce its degradation. We show that modelling the intracellular half-life of A3G can induce its Vif-independent targeting to the ubiquitin-proteasome system. By using various amino acids (X) in a cleavable ubiquitin-X-A3G fusion, we demonstrate that the half-life (t1/2) of X-A3G can be manipulated. We show that A3G molecules with a half-life of 13 min are incorporated into virions, whereas those with a half-life shorter than 5 min were not. The amount of X-A3G incorporated into virions increases from 13 min (Phe-A3G) to 85 min (Asn-A3G) and remains constant after this time period. Interestingly, despite the presence of similar levels of Arg-A3G (t1/2=28 min) and Asp-A3G (t1/2=65 min) into HIV-1 Deltavif virions, inhibition of viral infectivity was only evident in the presence of A3G proteins with a longer half-life (t1/2 > or = 65 min).

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