Function of human immunodeficiency virus type 1 Vpu protein in various cell types

We evaluated the function of human immunodeficiency virus type 1 vpu gene in various cell lines. We established a highly sensitive system consisting of chloramphenicol acetyltransferase and reverse transcriptase assays and used it to monitor the effects of mutation of the vpu gene. In some cell lines, Vpu protein was not required at the early phase of viral replication but was important for efficient virion production. In these cells, the Vpu protein functioned effectively irrespective of the presence of intact env gene products. Likewise, CD4 gene expression had no effects on Vpu function. In the other cell lines tested, Vpu protein was not important for virion release, and the vpu mutant clone generated a normal level of progeny virions upon transfection.