HUMAN IMMUNODEFICIENCY VIRUSES REGULATED BY ALTERNATIVE TRANS-ACTIVATORS - GENETIC-EVIDENCE FOR A NOVEL NON-TRANSCRIPTIONAL FUNCTION OF TATIN VIRION INFECTIVITY

Thirteen genetically altered HIV-l proviruses were created. These vari ous genomes can be segregated into three groups: (i) a set of tat(-) v iruses that have a functional HTLV-I Tax inserted in nef; (ii) a set o f tat(-) viruses,vith Gal4 binding sites inserted in U3 and a Gal4-VP1 6 cDNA inserted in nef; and (iii) a set of tat(+) HIV genomes that are 5 ' and 3 ' TAR(-) and are Gal4-binding-site(+) in U3 and Ga14-VP16() in nef. We found that viruses in groups (i) and (ii), although tat(- ), were fully complemented for viral gene expression based on quantita tive measurements of viral protein synthesis and on the visualization by electron microscopy of the proper assembly of morphologically corre ct virions. Interestingly, group (i) and (ii) virions were defective i n a spreading cytopathic infection when assayed in T-lymphocytes. Grou p (iii) viruses, although capable of producing intact Tat protein, als o could not use Tat for transcription/gene expression because of the T AR(-) genotype. However, this class of viral genomes produced viruses that were highly infectious and cytopathic in primary and in continuou sly propagated T-lymphocytes. These three groups of viruses are all tr anscriptionally Tat-TAR independent. Their distinct differences in inf ectivity/cytopathicity provide genetic evidence that Tat provides a tr anscriptionally independent function in determining infectivity and cy topathicity in the setting of a spreading viral infection. Given that all HIV virions normally contain four intact copies of TAR RNA, our fi ndings suggest a re-examination of whether Tat could be a virion-TAR-a ssociated protein and the possible implications of this for virus infe ctivity/cytopathicity.