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 (for chromatin condensation), various microtubule-associated proteins (for mitotic spindle formation) and lamins (degradation of nuclear envelope).
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.
Disassembly by APC
MPF is disassembled when anaphase-promoting complex (APC) polyubiquitinates cyclin B, marking them for degradation.