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Gene Review

FBXO5  -  F-box protein 5

Homo sapiens

Synonyms: EMI1, Early mitotic inhibitor 1, F-box only protein 5, FBX5, Fbxo31
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High impact information on FBXO5

  • CSF extracts immunodepleted of Emi1 degrade cyclin B, and exit from mitosis prematurely in the absence of calcium [1].
  • Emi1 is required to arrest unfertilized eggs at metaphase of meiosis II and seems to be the long-sought mediator of CSF activity [1].
  • Emi1 (early mitotic inhibitor) inhibits APC/C (anaphase-promoting complex/cyclosome) activity during S and G2 phases, and is believed to be required for proper mitotic entry [2].
  • These data suggest that Emi1 plays a critical role in preserving genome integrity by blocking rereplication, revealing a previously unrecognized function of this inhibitor of APC/C [2].
  • Rereplication upon Emi1 depletion activates the DNA damage checkpoint pathways [2].

Biological context of FBXO5


Anatomical context of FBXO5


Associations of FBXO5 with chemical compounds

  • The effect of rapamycin on the degradation rate of Skp2 expression was examined in cycloheximide-treated cells and in relationship to the anaphase promoting complex/Cdh1 (APC\C) inhibitor Emi1 [7].

Other interactions of FBXO5

  • Early mitotic inhibitor 1 (Emi1) inhibits the activity of the anaphase promoting complex/cyclosome (APC/C), which is a multisubunit ubiquitin ligase that targets mitotic regulators for degradation in exit from mitosis [3].
  • In this report, we show that Emi1 proteolysis can be induced by cyclin A/cdk (cdk for cyclin-dependent kinase) [5].
  • The RNAi method was used to dissect the early mitotic roles of meiotic regulators, which suggests that CDC20 is essential for the first mitotic division, while EMI1 and EMI2 are not essential for this process [8].
  • Here, we identify Pin1 as a new regulator of Emi1 that induces Emi1 stabilization by preventing its association with SCF(betatrcp) [5].
  • Paradoxically, Emi1 is stable during G2 phase, when cyclin A/cdk, Plx1 and SCF(betatrcp) (SCF for Skp1-Cul1-Fbox protein)-which play a role in its degradation-are active [5].

Analytical, diagnostic and therapeutic context of FBXO5

  • Using cell culture model systems, we found that Emi1 overexpression leads to proliferation, tetraploidy and genome instability of cells deficient for p53 [9].


  1. Emi1 is required for cytostatic factor arrest in vertebrate eggs. Reimann, J.D., Jackson, P.K. Nature (2002) [Pubmed]
  2. The APC/C inhibitor, Emi1, is essential for prevention of rereplication. Machida, Y.J., Dutta, A. Genes Dev. (2007) [Pubmed]
  3. Role of Polo-like kinase in the degradation of early mitotic inhibitor 1, a regulator of the anaphase promoting complex/cyclosome. Moshe, Y., Boulaire, J., Pagano, M., Hershko, A. Proc. Natl. Acad. Sci. U.S.A. (2004) [Pubmed]
  4. Plk1 regulates activation of the anaphase promoting complex by phosphorylating and triggering SCFbetaTrCP-dependent destruction of the APC Inhibitor Emi1. Hansen, D.V., Loktev, A.V., Ban, K.H., Jackson, P.K. Mol. Biol. Cell (2004) [Pubmed]
  5. Pin1 stabilizes Emi1 during G2 phase by preventing its association with SCF(betatrcp). Bernis, C., Vigneron, S., Burgess, A., Labb??, J.C., Fesquet, D., Castro, A., Lorca, T. EMBO Rep. (2007) [Pubmed]
  6. Bovine papillomavirus replicative helicase E1 is a target of the ubiquitin ligase APC. Mechali, F., Hsu, C.Y., Castro, A., Lorca, T., Bonne-Andrea, C. J. Virol. (2004) [Pubmed]
  7. The mTOR inhibitor rapamycin down-regulates the expression of the ubiquitin ligase subunit Skp2 in breast cancer cells. Shapira, M., Kakiashvili, E., Rosenberg, T., Hershko, D.D. Breast Cancer Res. (2006) [Pubmed]
  8. Injection of Mammalian Metaphase II Oocytes with Short Interfering RNAs to Dissect Meiotic and Early Mitotic Events. Amanai, M., Shoji, S., Yoshida, N., Brahmajosyula, M., Perry, A.C. Biol. Reprod. (2006) [Pubmed]
  9. Overexpression of the anaphase promoting complex/cyclosome inhibitor Emi1 leads to tetraploidy and genomic instability of p53-deficient cells. Lehman, N.L., Verschuren, E.W., Hsu, J.Y., Cherry, A.M., Jackson, P.K. Cell Cycle (2006) [Pubmed]
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