CDC2 Protein Kinase/metabolism; Cell Cycle Proteins/antagonists & inhibitors; Mitosis; Nuclear Proteins/antagonists & inhibitors; Protein-Tyrosine Kinases/antagonists & inhibitors; Xenopus Proteins/antagonists & inhibitors; cdc25 Phosphatases/antagonists & inhibitors; Animals; CDC2 Protein Kinase/antagonists & inhibitors; CDC2 Protein Kinase/genetics; Cell Cycle Proteins/genetics; Cell Cycle Proteins/metabolism; Cyclin B/genetics; Cyclin B/metabolism; Cyclin-Dependent Kinases/antagonists & inhibitors; Cyclin-Dependent Kinases/genetics; Cyclin-Dependent Kinases/metabolism; Feedback, Physiological/drug effects; Female; G2 Phase/drug effects; Gene Expression/drug effects; HeLa Cells; Humans; Membrane Proteins; Nuclear Proteins/genetics; Nuclear Proteins/metabolism; Phosphoprotein Phosphatases/antagonists & inhibitors; Phosphoprotein Phosphatases/genetics; Phosphoprotein Phosphatases/metabolism; Phosphorylation/drug effects; Prometaphase/drug effects; Protein Kinase Inhibitors/pharmacology; Protein Phosphatase 2/antagonists & inhibitors; Protein Phosphatase 2/genetics; Protein Phosphatase 2/metabolism; Protein Serine-Threonine Kinases/antagonists & inhibitors; Protein Serine-Threonine Kinases/genetics; Protein Serine-Threonine Kinases/metabolism; Protein-Tyrosine Kinases/genetics; Protein-Tyrosine Kinases/metabolism; S Phase/drug effects; Xenopus Proteins/genetics; Xenopus Proteins/metabolism; Xenopus laevis; cdc25 Phosphatases/genetics; cdc25 Phosphatases/metabolism