Tripartite motif-containing protein 5 also known as RING finger protein 88 is a protein that in humans is encoded by the TRIM5 gene. The alpha isoform of this protein, TRIM5α, is a retrovirus restriction factor, which mediates species-specific, early block to retrovirus infection.

The protein encoded by this gene is a member of the tripartite motif (TRIM) family. The TRIM motif includes three zinc-binding domains, a RING, a B-box type 1 and a B-box type 2, and a coiled-coil region. The protein forms homo-oligomers via the coilel-coil region and localizes to cytoplasmic bodies. It appears to function as a E3 ubiquitin-ligase and ubiqutinates itself to regulate its subcellular localization. It may play a role in retroviral restriction. Multiple alternatively spliced transcript variants encoding different isoforms have been described for this gene. [provided by RefSeq, Dec 2009].
Function: Isoform Alpha is a retrovirus restriction factor, which mediates species-specific, early block to retrovirus infection. Targets retroviral capsid soon after entry into the cell, and prevents reverse transcription of the virus RNA genome. Isoform Alpha trimers may make multiple contacts with the hexameric lattice of CA proteins which constitute the surface of retrovirion core, and somehow inactivate the virus. Restricts efficiently infection by N-MLV, but not HIV-1. May have E3 ubiquitin-protein ligase activity