Human immunodeficiency virus type 1 N-terminal capsid mutants that exhibitaberrant core morphology and are blocked in initiation of reverse transcription in infected cells

A group of conserved hydrophobic residues faces the interior of the coiled- coil-like structure within the N-terminal domain of the human immunodeficie ncy virus type 1 (HIV-1) capsid protein (CA). It has been suggested that th ese residues are important for maintaining stable structure and functional activity. To investigate this possibility, we constructed two HIV-1 clones, in which Trp23 or Phe40 was changed to Ala. We also constructed a third mu tant, D51A, which has a mutation that destroys a salt bridge between Pro1 a nd Asp51. All three mutants are replication defective but produce virus par ticles. Mutant virions contain all of the viral proteins, although the amou nt and stability of CA are decreased and levels of virion-associated integr ase are reduced. The mutations do not affect endogenous reverse transcripta se activity; however, the mutants are blocked in their ability to initiate reverse transcription in infected cells and no minus-strand strong-stop DNA is detected. The defect in reverse transcription is associated with striki ng defects in the morphology of mutant virus cores, as determined by transm ission electron microscopy. Our data indicate that the mutations made in th is study disrupt CA structure and prevent proper maturation of virus cores. We propose that this results in a defect in core stability or in an early postentry event preceding reverse transcription.