Note: this site last updated in 2006
An article from "The Molecules of HIV" (c) Dan Stowell
APOBEC3G is a protein found inside cells which has a very specific antiviral role:When a virus has infected a cell it forces it to produce new virus particles. But APOBEC3G sneaks into these newly-produced particles and makes them less infective by interfering with the replication of the viral genome when the particle finds its next victim.
(Exactly how does it interfere? During the reverse%20transcription">reverse transcription phase, it catalyses changes in the DNA copy of the viral genome, causing mistakes all along the genomic code.)
Not all cells contain APOBEC3G. Cells without APOBEC3G are sometimes called "permissive" cells since they allow HIV to replicate even without Vif.
Unfortunately for cells, HIV has a strategy for defeating APOBEC3G (the same strategy used by many other retroviruses">retroviruses). Its Vif protein specifically binds to APOBEC3G and causes its degradation.