Behavior of cyclin B and cyclin B-dependent kinase during starfish oocyte meiosis reinitiation: Evidence for non-identity with MPF

We reconsider the notion of MPF initiation, which is generally viewed as th e prerequisite production of a small cdc2-cyclin B kinase activity sufficie nt to trigger its own self-amplification. Using starfish oocytes as a tool, we show that H1 kinase activation is not explosive, but rather is a gradua l process in both time and space. We show further that the production of ev en a large H1 kinase activity, either in MPF-microinjected or in hormone-st imulated oocytes, is not sufficient to trigger MPF amplification. ((C) Else vier, Paris).