ABSTRACT
Although maturation-promoting factor (MPF) was first recognized within oocytes as a cytoplasmic activity mediating the action of maturation-inducing hormones, MPF is now established to be a dominant factor that governs the cell cycle progression in M-phase of all eukaryotic cells. Active MPF has recently been shown to be a complex of cyclin and a homolog of fission yeast cdc2 gene product. Immature oocytes contain cyclin B protein, which is destroyed at the end of first meiosis, accumulated at the second metaphase and then destroyed again. In contrast, cdc2 protein is present throughout the meiotic cycles. Cyclin exists in association with cdc2 protein in immature oocytes as well as in oocytes at each meiotic metaphase. The activation of MPF occurs in the complex of cdc2 and cyclin, and then the destruction of cyclin results in MPF inactivation.
