INCORPORATION OF FUNCTIONAL HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 INTEGRASE INTO VIRIONS INDEPENDENT OF THE GAG-POL PRECURSOR PROTEIN

Retroviral integrase (IN) is expressed and incorporated into virions a s part of the Gag-Pol polyprotein precursor. IN catalyzes integration of the proviral DNA into host cell chromosomes during the early stages of the virus life cycle, and as a component of Gag-Pol, it is involve d in virion morphogenesis during late stages. It is unknown whether th e scheme, conserved among retroviruses, for expressing and incorporati ng IN as a component of the Gag-Pol precursor protein is necessary for its function in the infected cell after viral entry. We have develope d human immunodeficiency virus (HIV) virion-associated accessory prote ins (Vpr and Vpx) as vehicles to deliver both foreign and viral protei ns into the virus particle by their expression in trans as heterologou s fusion proteins (X. Wu, et al., J. virol. 69:3389-3398, 1995; X. Wu, et al., J. Virol. 70:3378-3384, 1996; X. Wu, et al., EMBO J. 16:5113- 5122, 1977). To analyze IN function independent of its expression as a part of Gag-Pol, we expressed and incorporated IN into HIV type 1 (HI V-1) virions in trans as a fusion partner of Vpr (Vpr-IN). Our results demonstrate that the Vpr-IN fusion protein is efficiently incorporate d into virions and then processed by the viral protease to liberate th e IN protein. Virus derived from IN-minus provirus is noninfectious. H owever, this defect is overcome by trans complementation with the Vpr- IN fusion protein. Moreover, complemented virions are able to replicat e through a complete cycle of infection, included formation of the pro virus (integration). These results show, for the first time, that full IN function can be provided in trans, independent of its expression a nd incorporation into virions as a component of Gag-Pol. This finding also indicates that the IN domain of Gag-Pol is not required for the f ormation of infectious virions when IN is provided in trans. The abili ty to incorporate functional IN into retroviral particles in trans wil l provide unique opportunities to explore the function of this critica l enzyme in a biologically relevant context, i.e., in infected cells a s part of the nucleoprotein/preintegration complex.