Figure 2.

F-box protein functions. (a) The SCF complex. The F-box protein is linked to the SCF complex via interaction between the F-box and Skp1. A ubiquitin-conjugating enzyme (Ubc) binds to the SCF complex and transfers ubiquitin (Ub) onto substrates bound by the F-box protein. When the substrate becomes poly-ubiquitinated, it is degraded by the 26S proteasome. (b) Skp1 binds to the F-box of Ctf13, facilitating Ctf13 phosphorylation, which allows Ctf13 to form the structural core of the CBF3 centromere-binding complex. (c) The F-box of Elongin A binds Elongin C (El C). The association of Elongins B and C with A increases Elongin A transcriptional activity. (d) The FOG-2/GLD-1 complex binds the 3' UTR of tra-2 mRNA to translationally repress it. The function of the F-box of FOG-2 is currently unknown. (e) Cyclin F binds to cyclin B1-cdc2 through a direct association of the cyclin F 'cyclin box' with the CRS domain of cyclin B1, and may be required for cyclin B1 nuclear localization. The function of the F-box of cyclin F is unknown. NLS, nuclear localization signal.