RAF (also known as MAPKKK),  A ser/thr protein kinase

TLS Online TPP Program

#Id: 8873

#Unit 2. Cellular Organization

Cdc25B, activating an initial small pool of cyclin B/1 at the centrosome, which is facilitate centrosome maturation.

TLS Online TPP Program

#Id: 8874

#Unit 2. Cellular Organization

Initial pool of active cyclin B-CDK1 phosphorylates Cdc25C, this recruits Pin1 and Plk1, which recognize Cdc25C through their phospho-binding domains. 

TLS Online TPP Program

#Id: 8875

#Unit 2. Cellular Organization

Pin1 and Plk1 modify and phosphorylate Cdc25C to stimulate its phosphatase activity

TLS Online TPP Program

#Id: 8877

#Unit 2. Cellular Organization

The pool of active Cdc25C is created, that activates the large pool of cytosolic cyclin B-CDK1, which activates more cytosolic Cdc25C as part of positive feedback loop 1

TLS Online TPP Program

#Id: 8878

#Unit 2. Cellular Organization

At the same time that Cdc25C is being activated, mitotic CDKs and Plk1 phosphorylate Wee1, which targets it for destruction through a phosphobinding SCF protein-ubiquitin ligase. This forms positive feedback loop 2

TLS Online TPP Program

#Id: 8879

#Unit 2. Cellular Organization

This combination of two positive feedback loops:

one that activates a CDK1 activator (Cdc25C)

one that inhibits a CDK1 inhibitor (Wee1)

results in the abrupt and irreversible transition from G2 into mitosis.