Ribosomal Protein S6 Kinase Alpha 5 (RPS6Ka5)

The predicted 802-amino acid MSK1 protein contains 2 protein kinase domains, each of which includes the 11 subdomains characteristic of all protein kinases. MSK1 shares 43% protein sequence identity with the MAPKAP-K1 isoforms. Northern blot analysis indicated that MSK1 was expressed as a 4-kb mRNA in all tissues tested, with the highest levels of expression in brain, muscle, and placenta. Immunoelectron microscopy localized MSK1 to the nucleus.

MSK1 was activated in vitro and in vivo by either ERK or SAPK2 proteins. MSK1, rather than MAPKAP-K1 or MAPKAP-K2/K3, mediates activation of the cAMP response element-binding protein and activating transcription factor-1 by either growth factors or stress signals.