In addition to this catalytic core, Cdk1, like other cyclin-dependent kinases, contains a T-loop, which, in the absence of an interacting cyclin, prevents substrate binding to the Cdk1 active site.

SBF is inhibited by the protein Whi5; however, when phosphorylated by Cln3-Cdk1, Whi5 is ejected from the nucleus, allowing for transcription of the G1/S regulon, which includes the G1/S cyclins Cln1,2.

[11] G1/S cyclin-Cdk1 activity leads to preparation for S phase entry (e.g., duplication of centromeres or the spindle pole body), and a rise in the S cyclins (Clb5,6 in S. cerevisiae).

Finally, phosphorylation by M cyclins (e.g., Clb1, 2, 3 and 4) in complex with Cdk1 leads to spindle assembly and sister chromatid alignment.

This destruction of M cyclins leads to the final events of mitosis (e.g., spindle disassembly, mitotic exit).

A conserved tyrosine (Tyr15 in humans) leads to inhibition of Cdk1; this phosphorylation is thought to alter ATP orientation, preventing efficient kinase activity.

In S. pombe, for example, incomplete DNA synthesis may lead to stabilization of this phosphorylation, preventing mitotic progression.