p90 Rsk (ribosomal protein S6 kinase) is a 90 serine/threonine kinase and a member of the S6 kinase subfamily. This kinase is normally cytosolic but is transiently targeted to the membrane after activation. p90 Rsk phosphorylates a range of substrates including ribosomal protein S6 and is activated by the extracellular signal kinases ERK 1/2, PDK-1,and MAPK kinase cascade. p90 Rsk is phosphorylated and can interact with 14-3-3 beta, and ERK 1/2 under quiescent conditions p90 Rsk is decreased upon mitogen stimulation. The Poly6048 antibody recognizes the N-terminal region of human p90 Rsk and has been shown to be useful for Western blotting.