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 strain.

Formation of large syncytia and rapid cell killing are characteristics of the Zairian human immunodeficiency virus type 1 isolate HIV-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 determinants corresponding to the splice donor, the packaging signal, and the coding sequence of the p18gag protein together with the HIV-1-NDK EcoRI5278-XhoI8401 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 p18gag 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- cells 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.