RSK1, Active

The RSK (ribosomal S6 kinase) family comprises growth factor-regulated serine/threonine kinases, known also as p90(rsk). RSK1 contains 2 nonidentical kinase catalytic domains and phosphorylates various substrates, including members of the mitogen-activated kinase (MAPK) signalling pathway. Moller described the cloning and characterization of 3 genes encoding RSKs, and HU1 (also named RPS6KA1, or RSK1) cDNA encodes a predicted 735-amino acid protein containing 2 distinct consensus ATP-binding site sequences. Northern blot and RNase protection analyses detected an approximately 3.5-kb HU1 transcript in lymphocytes, skeletal muscle, liver, and adipose tissue (1). Zeniou determined the expression of the RSK1, RSK2, and RSK3 genes in various human tissues, during mouse embryogenesis, and in mouse brain (2). RSKs are implicated in the activation of the mitogen-activated kinase (MAPK) cascade and the stimulation of cell proliferation and differentiation (3).