The contribution of RING and B-box 2 domains to retroviral restriction mediated by monkey TRIM5α

TRIM5α is a cytoplasmic protein that mediates a post-entry block to infection by some retroviruses. TRIM5α contains a tripartite motif (TRIM), which includes RING, B-box 2, and coiled-coil domains, and a C-terminal B30.2 (SPRY) domain. We investigated the contribution of the RING and B-box 2 domains to the antiretroviral activity of rhesus monkey TRIM5α (TRIM5α_rh), which potently restricts infection by human immunodeficiency virus, type 1 (HIV-1) and simian immunodeficiency virus of African green monkeys (SIV_agm). Disruption of the RING domain caused mislocalization of TRIM5α_rh so that the cytoplasmic level of the protein was decreased compared with that of the wild-type protein. Nonetheless, partial ability to restrict HIV-1 and SIV_agm was retained by the RING domain mutants. By contrast, although TRIM5α _rh mutants with disrupted B-box 2 domains were efficiently expressed and correctly localized to the cytoplasm, antiretroviral activity was absent. The B-box 2 mutants colocalized and associated with wild-type TRIM5α_rh and exerted dominant-negative effects on the antiretroviral activity of the wild-type protein. Taken together with other data, these results indicate that functionally defective TRIM5α _rh molecules that retain a coiled coil can act as dominant-negative inhibitors of wild-type TRIM5α_rh function. The RING domain of TRIM5α_rh is not absolutely required for retrovirus restriction but can influence cytoplasmic levels of the protein and thus indirectly alter function. The B-box 2 domain, by contrast, appears to be essential for efficient retrovirus restriction.