This application will seek to better understand the mechanism by which the TRIM5alpha protein from rhesus macaques (rhTRIM5alpha) inhibits HIV-1 infection by defining the molecular and cellular biology of rhTRIM5alpha during restriction. We have identified a number of cellular proteins that associate with TRIM5alpha in cells. We have also developed powerful new methods to quantitatively characterize the association of TRIM5alpha with these cellular proteins. In the first aim, we will examine the connection between the ability of rhTRIM5alpha to self-associate and restrict retroviral infection. Specifically, we will characterize the effects of specific rhTRIM5alpha variants that have lost the ability to localize to cytoplasmic bodies due to specific mutations we have introduced into the linker2 region of the protein. We will identify the determinants in this region that mediate ability of rhTRIM5alpha to self-associate, measuring this ability with a novel, imaging based self-association assay we have recently developed. We will utilize the knowledge generated in these studies to develop rhTRIM5alpha variants with increased ability to restrict HIV-1 infection. In the second aim, we will define the role of the protein p62/sequestosome1 in regulating the degradation of TRIM5alpha. The known biological function of this protein, a scaffolding protein that mediates the shuttling of ubiquitylated cargo proteins to the proteasome, makes it an interesting candidate to play a role in the biology of TRIM5alpha mediated retroviral restriction. We will test the hypothesis that p62 conditionally regulates the ability of different cellular degradative pathways to degrade TRIM5alpha. In the third aim, we will use quantitative imaging methods to define the events that occur in cells when restriction sensitive virions enter the cytoplasm of target cells. By monitoring the presence of biologically relevant cellular proteins in TRIM5alpha cytoplasmic bodies during restriction, we will be able g restriction, we will be able to dissect and develop an understanding of this critical biological process.