Introduction of a mutation in the leucine zipper motif of the cytoplasmic domain of HIV-1 gp41. (a) Functional domains of gp41. Fusion, fusion peptide; TM, transmembrane domain; LLP1 and LLP2, lentivirus lytic peptides 1 and 2. The numbers 1–151 indicate residue positions in the cytoplasmic domain of HIV-1 gp41 (gp41c). The LZ motif is shown in single-letter amino acid code, with the leucines comprising the LZ motif highlighted. The numbers 512–854 indicate residue positions in the HIV-1 gp160 env polypeptide. The Rev open reading frame remains unchanged. The numbers 8592–8619 indicate nucleotide positions in the NL4-3 genome. (b) L95R replication in vitro was cell type-dependent. SupT1, PBMC, or CEMx174 cells were infected with equivalent RT units of NL4-3 or L95R. Virus replication (RT activity) was monitored every 3 days for 15 or 24 days postinfection. The data are representative of three (PBMC) or four (T-cell lines) experiments with similar replication kinetics.