Specific recognition and accelerated uncoating of retroviral capsids by the TRIM5α restriction factor

The host restriction factor TRIM5 alpha mediates species-specific, early blocks to retrovirus infection; susceptibility to these blocks is determined by viral capsid sequences. Here we demonstrate that TRIM5 alpha variants from Old World monkeys specifically associate with the HIV type 1 (HIV-1) capsid and that this interaction depends on the TRIM5 alpha B30.2 domain. Human and New World monkey TRIM5 alpha proteins associated less efficiently with the HIV-1 capsid, accounting for the lack of restriction in cells of these species. After infection, the expression of a restricting TRIM5 alpha in the target cells correlated with a decrease in the amount of particulate capsid in the cytosol. In some cases, this loss of particulate capsid was accompanied by a detectable increase in soluble capsid protein. Inhibiting the proteasome did not abrogate restriction. Thus, TRIM5 alpha restricts retroviral infection by specifically recognizing the capsid and promoting its rapid, premature disassembly.