Cyclophilin A incorporation is not required for human immunodeficiency virus type 1 particle maturation and does not destabilize the mature capsid

The cellular protein cyclophilin A (CypA) is packaged into human immunodefi ciency virus type 1 (HIV-1) virions through a specific interaction with the capsid (CA) domain of the Gag polyprotein. CypA is important for infectivi ty, but its role in viral replication is currently unknown. Previous report s suggested that CypA promotes uncoating or enhances maturation. We analyze d the morphology and capsid stability of HIV-1 variants defective in CypA b inding and of virus grown in the presence of cyclosporin. Both cyclosporin treatment and alteration of Gly89 or Pro90 in the CypA-binding site of CA c aused a 5- to 20-fold decrease in CypA incorporation. Virus produced from c yclosporin-treated cells and Variants G89V and G89A were 10- to 100-fold le ss infectious but exhibited normal virion morphologies with regular cone-sh aped capsids. Irregular capsid morphologies and lower infectivities were ob served for some other variants in the CypA-binding region. Decreased CypA i ncorporation did not reduce the kinetics of intracellular polyprotein proce ssing or of virus release. No increase in immature particles was observed. These results suggest that CypA does not promote virion maturation. Further more, detergent stripping of virus particles with various CypA contents rev ealed no difference in capsid stability. Based on these results and those r eported in the accompanying paper, it appears likely that CypA also is not an uncoating factor. Alternative models for CypA function are discussed, (C ) 1999 Academic Press.