Retroviral restriction factor TRIM5α is a trimer

The retrovirus restriction factor TRIM5 alpha targets the viral capsid soon after entry. Here we show that the TRIM5 alpha protein oligomerizes into trimers. The TRIM5 alpha coiled-coil and B30.2(SPRY) domains make important contributions to the formation and/or stability of the trimers. A functionally defective TRIM5a mutant with the RING and B-box 2 domains deleted can form heterotrimers with wild-type TRIM5 alpha, accounting for the observed dominant-negative activity of the mutant protein. Trimerization potentially allows TRIM5 alpha to interact with threefold pseudosymmetrical structures on retroviral capsids.