The Gag assembly-defective mutant MoGag was constructed by recombining the CA mutant M39A/W184A/M185A with NC mutant NC15A, which was kindly provided by P. Spearman [56] . NC15A has 15 NC-basic residues replaced with alanine. M39A/ W184A/M185A was created by overlapping PCR with the following mutagenic primers: for M39A, 59-CTGATAGCGCT-GAAAATGCGGGTATCA-39, and for W184A/M185A, 59-CAACAACGTTTCTGTAGCCGCATTTTTTAC-39. The Mo-Gag mutation was cloned into the indicated PR-leucine zipper constructs. As described previously, Gag/PR has deleted RT and IN coding sequences [23] . In D25, Arg is substituted for the PR catalytic residue Asp [20] . The backbone of all expression constructs is the HIV-1 proviral plasmid HIVgpt [57] .