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.
Interacting Selectively and Non Covalently with a Regulatory Transcription Factor and Also with the Basal Transcription Machinery in Order to Modulate Transcription. Cofactors Generally Do Not Bind the Template Nucleic Acid But Rather Mediate Protein Protein Interactions Between Regulatory Transcription Factors and the Basal Transcription Machinery.