HUMAN-IMMUNODEFICIENCY-VIRUS TYPE-I NEF INDEPENDENTLY AFFECTS VIRION INCORPORATION OF MAJOR HISTOCOMPATIBILITY COMPLEX CLASS-I MOLECULES AND VIRUS INFECTIVITY

We have recently reported that HIV-I Nef down-regulates the cell surfa ce expression of major histocompatibility complex class I (MHC-I) mole cules. MHC-I molecules are one of the predominant cellular proteins as sociated with HIV-I virions. Wild-type or nef-mutated HIV-I virions we re analyzed by immunoelectronic microscopy and Western blot for partic le-associated MHC-I molecules. The number of MHC-I molecules was signi ficantly higher in HIV-I virions produced in the absence of Nef than i n wild-type virions, indicating that Nef affects the incorporation of MHC-I molecules into virions. Wildtype HIV particles have been shown t o be more infectious than Nef(-) viruses. This difference was maintain ed when Nef(+) and Nef(-) virions devoid of MHC-I molecules were produ ced in Daudi-CD4 cells. Therefore, the enhancement of virion infectivi ty and the down-regulation of MHC-I represent independent biological p roperties of Nef. (C) 1997 Academic Press.