HTLV-III expression and production involve complex regulation at the levels of splicing and translation of viral RNA.

The African green monkey nonlymphoid cell line cos-1 produces infectious HTLV-III virus following transfection with biologically active molecular clones of HTLV-III. Transfected cos-1 cells produce large amounts of viral RNA and protein. We have used this rapid transfection system to study the regulatory functions and synthetic capacity of the HTLV-III genome, as well as mutants derived from it. Analysis of transfected lymphoid and nonlymphoid cell lines suggests that tat-III-mediated trans-activation of viral gene expression is operative predominantly, if not exclusively, at a posttranscriptional level. We have also identified an additional HTLV-III-encoded gene that controls viral gene expression through regulation of the relative proportions of the various viral RNA transcripts and is required for viral replication.