Ribosomal protein S6 (rpS6) is a component of the 40S ribosomal subunit and is therefore thought to be involved in regulating translation. While the true function of rpS6 is currently under investigation, studies have shown that it is involved in the regulation of cell size, cell proliferation, and glucose homeostasis. Important S6 ribosomal protein phosphorylation sites include several residues (Ser235, Ser236, Ser240, and Ser244) located within a small, carboxy-terminal region of the S6 protein.

S6 Ribosomal Protein (S6RP) is the S6 subunit of the 40S ribosome and it functions to increase translation of mRNA containing a 5′-terminal oligopyramidine tract (5′-TOP). 1 mRNA with a 5’-TOP generally encode proteins involved in the translational machinery, such as proteins involved in ribosome formation. S6RP functions to control translation of proteins which are constituents of the ribosome, and therefore helps to control overall levels of protein translation. The function of S6RP is phosphorylation dependent, and S6RP is phosphorylated by P70S6K in a mitogen dependent fashion.