Each actin subunit (globular or G-actin) is a 375-amino-acid polypeptide contains a Mg+2 ion complexed with either ATP or ADP

TLS Online TPP Program

#Id: 8606

#Unit 2. Cellular Organization

M phase Cyclin–CDKs

In human - cyclin A-CDK 1

cyclin B-CDK 1

In budding yeast - CIb 1/2/3/4-Cdc 28

TLS Online TPP Program

#Id: 8607

#Unit 2. Cellular Organization

Cdk1 

=Cdc2 (vertebrates and fission yeast)

= Cdc28  (budding yeast)

TLS Online TPP Program

#Id: 8608

#Unit 2. Cellular Organization

There are three D cyclins in mammals:

cyclins D1, D2, and D3

TLS Online TPP Program

#Id: 8609

#Unit 2. Cellular Organization

In free CDK2, the A-loop blocks access of protein substrates to the γ phosphate of the bound ATP.

TLS Online TPP Program

#Id: 8610

#Unit 2. Cellular Organization

TLS Online TPP Program

#Id: 8611

#Unit 2. Cellular Organization

Nonphosphorylated CDK bound to one of its cyclin partners has minimal but detectable protein kinase activity in vitro, although it may be essentially inactive in vivo.