NEUROVIRULENT SIMIAN IMMUNODEFICIENCY VIRUS INCORPORATES A NEF-ASSOCIATED KINASE-ACTIVITY INTO VIRIONS

We have demonstrated that a molecular clone, SIV/17E-Fr, is neurovirul ent in vivo and molecular analyses of this virus in primary macrophage s and neuroendothelial cells mapped the domains critical for this phen otype to the transmembrane and Nef proteins, The Nef protein is crucia l for virus replication and pathogenesis in SIV-infected rhesus macaqu es, In addition, both HIV and SIV require full-length Nef proteins for efficient virus replication in primary cells and optimal virion infec tivity, To characterize further the contribution of Nef to enhanced in fectivity and replication, we analyzed virus particles from a number o f SIV recombinant clones, These clones contained nef genes derived fro m either a lymphocyte-tropic (SIV(mac)239) or neurovirulent (SIV/17E-F r) virus or a nef gene with a premature stop codon or deletion, Immuno precipitation of Nef from virus particles revealed that SIV Nef is inc orporated into virions, Incorporation of the Nef protein was dependent on the presence of the N-terminal myristoylation sequence in the nef gene, In addition, enhanced replication and virion infectivity was ass ociated only with viruses containing the full-length Nef protein, To i nvestigate a potential mechanism of virion modification by Nef, in vit ro kinase assays were performed on the virion-derived Nef protein, Nef -associated kinase activity was detected only in virions containing Ne f sequences derived from the neurovirulent virus SIV/l7E-Fr, Thus, the se results suggest that selection for specific nef sequences occurs in vivo and has a significant effect on virus replication in specific ce lls and organs.