DN forms of class E proteins used in this experiment. A. DN forms of Vps4A and Vps4B. Both Vps4AEQ and Vps4BEQ have point mutations that render them defective in ATP hydrolysis. B. DN forms of AIP1/Alix. AIP1/Alix is composed of three major domains: Bro1 domain, V domain, and PRR (proline-rich region) . The role of AIP1/Alix in endosomal sorting and virus budding requires binding the ESCRT-III component CHMP4 at the broad Bro1 domain and the ESCRT-I component Tsg101 at the PRR. HIV-1 p6 and EIAV p9 bind to the V domain.