The anti-retroviral restriction factor TRIM5alpha contains the RING domain, which is frequently observed in E3 ubiquitin ligases. It was previously proposed that TRIM5alpha restricts human immunodeficiency virus type 1 (HIV-1) via proteasome-dependent and -independent pathways. Here we examined the effects of RING domain mutations on retrovirus restriction by TRIM5alpha in various combinations of virus and host species. Simian immunodeficiency virus isolated from macaque (SIVmac) successfully avoided attacks by RING mutants of African green monkey (AGM)-TRIM5alpha that could still restrict HIV-1. Addition of proteasome inhibitor did not affect the anti-HIV-1 activity of AGM-TRIM5alpha, whereas it disrupted at least partly its anti-SIVmac activity. In the case of mutant human TRIM5alpha carrying proline at the position 332, however, both HIV-1 and SIVmac restrictions were eliminated as a result of RING domain mutations. These results suggested that the mechanisms of retrovirus restriction by TRIM5alpha vary depending on the combination of host and virus.
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