Although myristylation is required for Gag membrane binding (which may in turn promote efficient Gag multimerization [32] ), we found evidence that myr-Gag/Pol or MoGag/Pol were capable of mediating Pr55 gag processing (Figs. 5 and 6 ). This finding suggests that neither membrane association nor an assembly-competent Gag domain is essential for the activation of PR embedded in Gag-Pol. It is likely that myr-Gag-Pol can still undergo dimerization to a level that is sufficient to trigger PR activation. Previous studies have shown that myr-Gag-Pol can efficiently cleave Pr55 gag in trans and be packaged into Pr55 gag VLPs [4, 7, 35] . The multimerization defect as a result of membrane binding apparently does not significantly compromise the LZ enhancement of PR-mediated Gag cleavage.