Note: this site last updated in 2006
An article from "The Molecules of HIV" (c) Dan Stowell
"Viral protein U" helps with the assembly of new virus particles, and helps them to bud from the host cell. It's possible for HIV to replicate and bud without this particular protein, but only 10% or 20% as many new virus particles are produced.
Vpu also works within the infected cell to enhace the degradation of CD4 proteins. This has the effect of reducing the amount of CD4 sticking out of the infected cell, therefore reducing the likelihood of superinfection.
Without the vpu gene, HIV virus actually kills its host cell quicker! A secondary effect of vpu is to delay the cytopathic (cell-killing) effects of virus infection, keeping the cell alive slightly longer so that it can produce more virus particles.
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