Question

How do you suppose mpf activity can be absent from immature oocytes yet appear in activated eggs, even when protein synthesis has been blocked by cycloheximide?

Answer 1

The appearance of MPF activity in the absence of protein synthesis suggests that an inactive precursor of MPF is being activated. In principle, activation could involve one of several kinds of post-translational modifications such as protease cleavage or changes in protein phosphorylation. From class you know that MPF is held in an inactive state by phosphorylation of an inhibitory site of Cdk. MPF is activated when that inhibitory phosphate is removed by the protein phosphatase, Cdc25.