Determinants for the rhesus monkey TRIM5alpha-mediated block of the late phase of HIV-1 replication.

Rhesus monkey TRIM5alpha (TRIM5alpharh) includes RING, B-box, coiled-coil, and B30.2(PRYSPRY) domains and blocks HIV-1 infection by targeting HIV-1 core through a B30.2(PRYSPRY) domain. Previously, we reported that TRIM5alpharh also blocks HIV-1 production in a B30.2(PRYSPRY)-independent manner. Efficient encapsidation of TRIM5alpharh, but not human TRIM5alpha (TRIM5alphahu), in HIV-1 virus-like particles suggests the interaction between Gag and TRIM5alpharh during viral assembly. Here, we determined responsible regions for late restriction activity of TRIM5alpharh. The RING disruption, but not the replacement with human TRIM21 RING, ablated the efficient encapsidation and the late restriction, suggesting that a RING structure was essential for the late restriction and efficient interaction with HIV-1 Gag. The prominent cytoplasmic body formation of TRIM5alpharh, which depended on the coiled-coil domain and the ensuing linker 2 region, was not required for the encapsidation. Intriguingly, TRIM5alpharh coiled-coil domain mutants (M133T and/or T146A) showed impaired late restriction activity, despite the efficient encapsidation and cytoplasmic body formation. Our results suggest that the TRIM5alpharh-mediated late restriction involves at least two distinct activities as follows: (i) interaction with HIV-1 Gag polyprotein through the N-terminal, RING, and B-box 2 regions of a TRIM5alpharh monomer, and (ii) an effector function(s) that depends upon the coiled-coil and linker 2 domains of TRIM5alpharh. We speculate that the TRIM5alpharh coiled-coil region recruits additional factor(s), such as other TRIM family proteins or a cellular protease, during the late restriction. RBCC domains of TRIM family proteins may play a role in sensing newly synthesized viral proteins as a part of innate immunity against viral infection.