A Membrane Bounded Organelle of Eukaryotic Cells in Which Chromosomes Are Housed and Replicated. in Most Cells the Nucleus Contains All of the Cell's Chromosomes Except the Organellar Chromosomes and Is the Site of RNA Synthesis and Processing. in Some Species or in Specialized Cell Types RNA Metabolism or DNA Replication May Be Absent.
Catalysis of the Reaction: a Phosphoprotein + H2o = a Protein + Phosphate. Together with Protein Kinases These Enzymes Control the State of Phosphorylation of Cell Proteins and Thereby Provide an Important Mechanism For Regulating Cellular Activity.