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

TRIM5 alpha is a cytoplasmic protein that mediates a post-entry block to infection by some retroviruses. TRIM5 alpha 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 TRIM5 alpha (TRIM5 alpha(rh)), which potently restricts infection by human immunodeficiency virus, type 1 (HIV-1) and simian immunodeficiency virus of African green monkeys (SIVagm). Disruption of the RING domain caused mislocalization of TRIM5 alpha(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 SIVagm was retained by the RING domain mutants. By contrast, although TRIM5 alpha(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 TRIM5 alpha(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 TRIM5 alpha(rh) molecules that retain a coiled coil can act as dominant-negative inhibitors of wild-type TRIM5 alpha(rh) function. The RING domain of TRIM5 alpha(rh) is not absolutely required for retrovirus restriction.