It resides exclusively in the nucleus because of a single monopartite nuclear localisation sequence (NLS) comprising amino acids 82-85 in the N-terminal domain.

SCF (Cdc4) dimerization hardly affects the affinity for target molecules, but significantly increases ubiquitin conjugation.

The SCF (Cdc4) complex has a regulatory function in cell cycle progression, signal transduction, and transcription.

[8] In order for the cell cycle to proceed, several inhibitory proteins, as well as cyclins, have to be eliminated at given time points.

[citation needed] Some important interactions in which Cdc4 is involved are: Swi5 is a transcriptional activator of Sic1, which inhibits S-phase CDKs.

[8] In order for the substrate adapter unit Cdc4 to bind to Sic1, a minimum of any six of the nine cyclin-dependent kinase sites on Sic1 have to be phosphorylated.

As recently stated, this "suggests that the ultrasensitivity in the Sic1-Cdc4 system may be driven at least in part by cumulative electrostatic interactions".

[10] Thus, ultrasensitivity allows a highly sensitive response: A graded input can be transformed into a sharply thresholded output.

The development of B-type cyclin–cyclin-dependent kinase activity, as well as the onset of DNA replication, requires degradation of Sic1 in the late G1 phase of the cell cycle.

Hence, in this case ultrasensitivity allows precise definition ("fine tuning") of the time point in which destruction of Sic1 occurs, leading to initiation of the next step in the cell cycle (-> DNA replication).

In general, the second degradation complex involved in cell cycle progression, APC, is responsible for proteolysis at that stage.

In addition to those functions mentioned above, Cdc4 is involved in some other degradation-dependent events in S. cerevisiae like for instance unfolded protein response.

[13] E3 has an additional function to its primary role in the degradation of certain cell cycle regulators: It is also involved in formation of the neural crest.