Phosphorylation of nuclear and cytoplasmic pools of ribosomal protein S6 during cell cycle progression.

Of all known ribosomal proteins, the 40S ribosomal protein S6 is by far the most extensively studied. Still, little is known about some basic aspects of S6 regulation including its cell cycle-related expression and localization. Using a flow cytometric single cell approach applied to whole cells and isolated nuclei, we monitored nucleocytoplasmic expression of total and S240/4 phosphorylated S6 during unperturbed cell cycle progression, providing first evidence for a S6-specific spatiotemporal pattern and its deregulation under conditions of hyperactivated mTOR.