Maturation promoting factor

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Maturation promoting factor (abbreviated MPF, also called mitosis-promoting factor or M-Phase promoting factor) is a heterodimeric protein composed of cyclin B and cyclin-dependent kinase (CDK1, also known as Cdc2) that stimulates the mitotic and meiotic cell cycles. MPF promotes the entrance into mitosis from the G2 phase by phosphorylating multiple proteins needed during mitosis. MPF is activated at the end of G₂ by a phosphatase, which removes an inhibitory phosphate group added earlier.

Targets of MPF include:

condensins, which enable chromatin condensation (see prophase)
various microtubule-associated proteins involved in mitotic spindle formation
lamins, interaction contributing to degradation of the nuclear envelope
Histones, H1 and H3
Golgi matrix, to cause fragmentation

[edit] Inhibition of myosin

MPF phosphorylates inhibitory sites on myosin early in mitosis. This prevents cytokinesis. When MPF activity falls at anaphase, the inhibitory sites are dephosphorylated and cytokinesis proceeds.