MX2 and infection: By generating cells containing endogenous mutations in CypA that affect CA recognition, we demonstrate that the effects of CypA (and CsA treatment) on HIV-1 and HIV-1 CA mutant infection and MX2 sensitivity are the direct result of interactions with CA, and do not appear to involve interactions between CypA and other cellular proteins (Figs 1, S2, S4, and S5).