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 or p34 kinase) 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.

MPF is made of 2 subunits:

• a subunit that transfers phosphate groups from ATP to specific serine and threonine residues of specific proteins (kinase activity)
• cyclin, a regulatory subunit

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.

[edit] Disassembly by APC

MPF is disassembled when anaphase-promoting complex (APC) polyubiquitinates cyclin B, marking it for degradation.

[edit] External links

• MeSH Maturation-Promoting+Factor

v • d • e Cell cycle proteins Cyclin A - B - D - E Cyclin-dependent kinase 2 - 3 - 4 - 5 - 6 - 7 - 8 - 9 - 10 - CDK-activating kinase Cyclin-dependent kinase inhibitor protein p14arf/p16INK4a - p21 - p27 - p57 Other Cdc2 - Cdc25 - Cdc42 - Cellular apoptosis susceptibility protein - E2F - Maturation promoting factor - Wee