Mitogenesis and protein synthesis: a role for ribosomal protein S6 phosphorylation?

It has been known for 20 years that the ribosomal protein S6 is rapidly phosphorylated when cells are stimulated to grow or divide. Furthermore, numerous studies have documented that there is a strong correlation between increases in S6 phosphorylation and protein synthesis, leading to the idea that S6 phosphorylation is involved in up-regulating translation. In an attempt to define a mechanism by which S6 phosphorylation exerts translational control, other studies have focused on characterizing the sites of phosphorylation of this protein and its location within the ribosome. Recent data show that S6 is a protein which may have diverse cellular functions and is essential for normal development, and that it may be involved in the translational regulation of a specific class of messages.