Cytoplasmic localization of the HTLV-III 3' orf protein in cultured T cells.

HTLV-III, the etiological agent of the acquired immunodeficiency syndrome, contains in its genome coding regions for several novel proteins. One of these, the 3' open reading frame (3'orf) encodes proteins of 26-27 kDa which are expressed in infected cells both in vivo and in vitro. A specific antiserum has been raised against the recombinant 3'orf protein synthesized in bacteria and used to localize the viral proteins by subcellular fractionation and immunofluorescence on HTLV-III infected cells. The antiserum specifically immunoprecipitated the 26- to 27-kDa proteins from both the cytoplasmic (S100) and the membrane fractions, with an enrichment in the latter. The proteins were not detected in the nucleus or organelle (S100 pellet) fractions. These proteins were also recognized in the same subcellular fractions by human sera from patients with AIDS. Indirect immunofluorescence on fixed infected cells confirmed the presence of the proteins in the cytoplasm. Immunoprecipitation and Western blot analysis of total proteins from disrupted HTLV-III virions with the specific antiserum failed to detect the 3'orf protein products, suggesting that they are not a major component of mature virions and may be involved in the intracellular regulation of viral replication.