MoBio MPF and the Initiation of Mitosis Chapter 8

The morphological changes in early mitosis are mainly due to the phosphorylation of related proteins catalyzed by MPF (mitosis promoting factor), which is actually the Cyclin B/Cdk1 complex. The activated MPF may phosphorylate histone protein H1 to condense chromatin. It can also phosphorylate nuclear lamins to break nuclear envelope. The microtubule structure is regulated by microtubule-associated proteins (MAPs) which can also be phosphorylated by MPF, resulting in the formation of the spindle.

The activity of MPF depends on its phosphorylation state, as shown in the following figure.

Image

Figure 8-B-2. The phosphorylation state of MPF (CycB-Cdc2 complex) and its activity. Cdc2 is a synonym for Cdk1. Y and T represent the specific Tyrosine and Threonine residue, respectively. MPF is active only when it is mono-phosphorylated at the specific Threonine residue.