A domain directly C-terminal to the major homology region of human immunodeficiency type 1 capsid protein plays a crucial role in directing both virus assembly and incorporation of Gag–Pol

We demonstrate here that a deletion of 14 amino acid residues directly C-terminal to the major homology region (MHR) of the HIV-1 capsid (CA) in Gag–Pol markedly affects the incorporation of Gag–Pol into virions. The 14-amino acid deletion also significantly impaired virus assembly. In agreement with previous reports, mutations at the very C-terminus of CA resulted in a remarkable reduction in virus production. However, HIV-1 Gag–Pol precursors containing the C-terminal CA mutation were still capable of being incorporated into virions at a level of about 50% that of the wild-type. These results suggest that the domain immediately C-terminal to the MHR is functionally involved in Gag–Gag and Gag/Gag–Pol interaction, and this supports the notion that Gag or Gag–Pol mutants blocked in assembly into virus particles can be rescued into virions provided they retain the domains that are able to interact with the Gag precursor. An HIV-1 Gag–Pol deletion mutant retaining a minimal sequence consisting of the MHR and the adjacent CA-SP1 was efficiently incorporated into virions. Analysis by immunofluorescence staining indicated that the subcellular localization patterns shown by the Gag–Pol mutants were not fully compatible with their efficiency in being incorporated into virions, suggesting that the ability of Gag–Pol mutants to be incorporated into virions largely depends on their interactions with the Gag precursor.