Apc5 is a subunit of the anaphase-promoting complex/cyclosome (APC/C) which is a multi-subunit ubiquitin ligase that mediates the proteolysis of cell cycle proteins in mitosis and G1. Apc5, although it does not harbour a classical RNA binding domain, Apc5 binds the poly(A) binding protein (PABP), which directly binds the internal ribosome entry site (IRES) of growth factor 2 mRNA. PABP was found to enhance IRES-mediated translation, whereas Apc5 over-expression counteracted this effect. In addition to its association with the APC/C complex, Apc5 binds much heavier complexes and co-sediments with the ribosomal fraction [1,2]. The N-terminus of Afi1 serves to stabilise the union between Apc4 and Apc5, both of which lie towards the bottom-front of the APC [3]. This region of the Apc5 member proteins carries a TPR-like motif.

1: The Apc5 subunit of the anaphase-promoting complex/cyclosome interacts with poly(A) binding protein and represses internal ribosome entry site-mediated translation. Koloteva-Levine N, Pinchasi D, Pereman I, Zur A, Brandeis M, Elroy-Stein O; Mol Cell Biol. 2004;24:3577-3587. PMID:15082755

2: The anaphase promoting complex/cyclosome: a machine designed to destroy. Peters JM; Nat Rev Mol Cell Biol. 2006;7:644-656. PMID:16896351

3: The transcription factor Atf1 binds and activates the APC/C ubiquitin ligase in fission yeast. Ors A, Grimaldi M, Kimata Y, Wilkinson CR, Jones N, Yamano H; J Biol Chem. 2009;284:23989-23994. PMID:19584054