Maturation promoting factor

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.

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

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.