The human immunodeficiency virus (HIV) gag gene product p18 is responsible for enhanced fusogenicity and host range tropism of the highly cytopathic HIV-1-NDK

Formation of large syncytia and rapid cell killing are characteristics of the Zairian human immunodeficiency virus type 1 isolate HlV-1-NDK, which is highly cytopathic for CD4+ lymphocytes in comparison with the HIV-1-LAV prototype. Chimeric viruses containing different combinations of HIV-1-NDK genetic determi-nants corresponding to the splice donor, the packaging signal, and the coding sequence of the p189ff protein together with the HIV-1-NDK EcoRI5278-XoI1840 fragment were obtained by polymerase chain reaction-directed recombination. Phenotypic analysis of recombinant viruses indicated that 75 amino acids from the N-terminal part of HIV-1-NDK p189 " protein together with the HIV-1-NDK envelope glycoprotein are responsible for enhanced fusogenicity of HIV-1-NDK in CD4+ lymphocytes as well as for enhanced infectivity of HIV-1-NDK in some CD4- cell lines. The HIV-1-NDK splice donor/packaging sequence and the sequence encoding the gag protein p25 were not important for the variation observed in HIV-1 fusogenicity. Human immunodeficiency virus type 1 (HIV-1) isolate