Structure and Function of HIV-1 Vpu

Aside from the typical retroviral gag, pol, and env genes, HIV encodes a series of accessory genes, vif, vpr, vpx, vpu, and nef. The vpu gene is found exclusively in HIV-1 (Strebel et al., 1988; Cohen et al, 1988; Matsuda, 1988). In tissue culture systems, defects in accessory genes are frequently not correlated with a detectable impairment of virus replication and, as a result, these genes are often referred to as “non-essential”. However, as more and more information on the function of the accessory proteins becomes available it also becomes increasingly clear that in vivo, these proteins indeed exert important functions. With respect to Vpu, Li et al found that macaques infected with Vpu-negative simian-human immunodeficiency virus chimeras (SHIV) had lower virus loads than Vpu-positive virus (Li et al., 1995). Also, using a SCID-hu model, Aldrovandi & Zack demonstrated that deletion of Vpu significantly affects virus infectivity and, to a somewhat lesser extend, pathogenicity of HIV (Aldrovandi & Zack, 1996). Thus, while there is currently only limited information available on the importance of Vpu in vivo, such model systems might be useful in investigating the in vivo relevance of Vpu. This article attempts to provide a brief overview on our current understanding of this viral accessory factor. More exhaustive reviews on Vpu can be found elsewhere (Jabbar, 1995; Bour et al., 1995a; Trono, 1995).