REMOVAL OF HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-1 (HIV-1) PROTEASE INHIBITORS FROM PREPARATIONS OF IMMATURE HIV-1 VIRIONS DOES NOT RESULT IN AN INCREASE IN INFECTIVITY OR THE APPEARANCE OF MATURE MORPHOLOGY

The processing of gag and gag-pol polyproteins by human immunodeficien cy virus type 1 (HIV-1) protease is a crucial step in the formation of infectious HIV-1 virions. In this study, we examine whether particles produced in the presence of inhibitors of HIV-1 protease can subseque ntly undergo gag polyprotein cleavage with restoration of infectivity following removal of the inhibitors, Viral particles produced during 7 days of culture in the presence of the protease inhibitors KNI-272 (1 0 mu M) and saquinavir (5 mu M) contained predominantly p55(gag) polyp rotein but little or no p24(gag) cleavage product, Following resuspens ion of the particles in medium free of the inhibitor, some gag polypro tein processing was detected in particles produced from the KNI-272-tr eated cells, but not from the saquinavir-treated cells within the firs t 3 h. However, the majority of the protein remained as p55(gag) throu ghout a 48-h experimental period, The infectivity (50% tissue culture infective dose per milliliter) of the viral particles from KNI-272-tre ated cells was 10(6)-fold lower than that of control particles and did not significantly increase over the 48 h after the inhibitor was remo ved, despite the apparent return of protease function in a subset of t hese virions, This failure to restore infectivity was due neither to a reduction in the number of particles produced by protease inhibitor-t reated cells nor to a failure of HIV RNA to be packaged in the virions . These particles also failed to express the mature phenotype by elect ron microscopy, Thus, while some processing of the gag polyprotein can occur in isolated HN virions, this does not appear to be sufficient t o restore infectivity in the majority of particles, This finding sugge sts that there may be constraints on postbudding polyprotein processin g in the production of viable particles. These results should have pos itive implications regarding the use of protease inhibitors as anti-HN drugs.