Integration into the host genome is one of the hallmarks of the retroviral life cycle and is catalyzed by virus-encoded integrases. While integrase has strict sequence requirements for the viral DNA ends, target site sequences have been shown to be very diverse. We carefully examined a large number of integration target site sequences from several retroviruses, including human immunodeficiency virus type 1, simian immunodeficiency virus, murine leukemia virus, and avian sarcoma-leukosis virus, and found that a statistical palindromic consensus, centered on the virus-specific duplicated target site sequence, was a common feature at integration target sites for these retroviruses.

Human TRIM5␣ (TRIM5␣ hu ) only modestly inhibits human immunodeficiency virus type 1 (HIV-1) and does not inhibit simian immunodeficiency virus (SIV mac ). Alteration of arginine 332 in the TRIM5␣ hu B30.2 domain to proline, the residue found in rhesus monkey TRIM5␣, has been shown to create a potent restricting factor for both HIV-1 and SIV mac. Here we demonstrate that the potentiation of HIV-1 inhibition results from the removal of a positively charged residue at position 332 of TRIM5␣ hu. The increase in restricting activity correlated with an increase in the ability of TRIM5␣ hu mutants lacking arginine 332 to bind HIV-1 capsid complexes. A change in the cyclophilin A-binding loop of the HIV-1 capsid decreased TRIM5␣ hu R332P binding and allowed escape from restriction. The ability of TRIM5␣ hu to restrict SIV mac could be disrupted by the presence of any charged residue at position 332. Thus, charged residues in the v1 region of the TRIM5␣ hu B30.2 domain can modulate capsid binding and restriction potency. Therapeutic strategies designed to neutralize arginine 332 of TRIM5␣ hu might potentiate the innate resistance of human cells to HIV-1 infection.Primates express dominant restriction factors that block retrovirus infection soon after entry but prior to reverse transcription (1, 2, 5). Genetic studies of virus variants and restriction factor competition studies indicate that the viral capsid is the determinant of susceptibility to restriction (3, 3b, 6, 13, 14). Most early restriction in primates is mediated by TRIM5␣ (7,10,16,23,26). TRIM5␣ is a member of the tripartite motif family of proteins and contains RING, B-box 2, and coiled-coil (RBCC) domains (17). TRIM5␣ also contains a C-terminal B30.2/SPRY domain, which is required for retroviral restriction (23). Deletion of the B30.2 domain disrupts the ability of the TRIM5␣ protein to bind viral capsid complexes (20,24). Differences in the B30.2 domains of TRIM5␣ proteins from distinct primate species account for patterns of retrovirus restriction. For example, the rhesus monkey TRIM5␣ (TRIM5␣ rh ) potently blocks human immunodeficiency virus type 1 (HIV-1), which is only weakly inhibited by human TRIM5␣ (TRIM5␣ hu ) (23). Neither TRIM5␣ rh nor TRIM5␣ hu efficiently restricts simian immunodeficiency virus (SIV mac ) (23). Four variable regions (v1 to v4) are found in the B30.2 domains of TRIM5␣ proteins from different primates (19,21). Differences in the v1 regions of TRIM5␣ rh and TRIM5␣ hu account for the differences in anti-HIV-1 potency of these TRIM5␣ variants (15,19,24,27). Alteration of arginine 332 in the v1 region of TRIM5␣ hu to the proline residue found in TRIM5␣ rh results in a protein that can potently restrict HIV-1 and, surprisingly, SIV mac infection (24, 27). Here we investigate the specific v1 sequences in TRIM5␣ hu required for efficient antiviral activity against HIV-1 and SIV mac and provide a mechanistic explanation for the observed enhancement of restriction that results from changes in this region. MATERIALS AND METHODS Plasmids a...

The coiled-coil domain of the tripartite motif (TRIM) family protein TRIM5alpha is required for trimerization and function as an antiretroviral restriction factor. Unlike the coiled-coil regions of other related TRIM proteins, the coiled coil of TRIM5alpha is not sufficient for multimerization. The linker region between the coiled-coil and B30.2 domains is necessary for efficient TRIM5alpha trimerization. Most of the hydrophilic residues predicted to be located on the surface-exposed face of the coiled coil can be altered without compromising TRIM5alpha antiviral activity against human immunodeficiency virus (HIV-1). However, changes that disrupt TRIM5alpha trimerization proportionately affect the ability of TRIM5alpha to bind HIV-1 capsid complexes. Therefore, TRIM5alpha trimerization makes a major contribution to its avidity for the retroviral capsid, and to the ability to restrict virus infection.