176 Host Factors in HIV Budding Heinrich Gottlinger*1, B Strack2, A Calistri2, E Popova1, and A Zamborlini2 1Univ of Massachusetts Med Sch, Worcester, USA and 2Dana-Farber Cancer Inst, Boston, MA, USA

HIV-1 budding from the plasma membrane requires a membrane fission event to separate the fully assembled viral particle from the host cell. The detachment of the virion is mediated by the p6 region of Gag, which harbors the so-called late assembly domain of HIV-1. The late assembly domain engages the host protein Tsg101, a component of the class E vacuolar protein sorting (Vps) pathway that normally functions in an endosomal budding event. Our results show that HIV-1 p6 additionally binds AIP1, another class E Vps protein. AIP1 interacts both with Tsg101 and with a component of the late-acting endosomal sorting complex ESCRT-III, which appears to be at the core of the cellular machinery that mediates HIV-1 budding. Defective versions of AIP1 and of ESCRT-III components block the final stage of HIV-1 release from the cell surface, a phenotype that closely resembles that of HIV-1 late domain mutants. In the case of the ESCRT-III component CHMP3, which is reported to interact with phosphatidylinositol 3,5-bisphosphate, this dominant negative activity against HIV-1 budding does not require an intact phosphoinosite binding site. Our results support a model in which CHMP proteins are tightly regulated by intramolecular interactions between their differentially charged N- and C-terminal domains, and their antiviral activity is triggered by mutations which disrupt these autoinhibitory interactions.