Serine/threonine-protein kinase 4 encodesacytoplasmickinasewithastructuresimilartoyeastSte20pkinase(anenzymethatcatalyzesthetransferofphosphategroupsfromhigh-energy,phosphate-donatingmoleculestospecificsubstrates).
In biochemistry, a kinase is an enzyme that catalyzes the transfer of phosphate groups from high-energy, phosphate-donating molecules to specific substrates. The protein encoded by this gene is a cytoplasmic kinase that is structurally similar to the yeast Ste20p (sterile 20 protein) kinase, which acts upstream of the stress-induced mitogen-activated protein kinase (MAPK) cascade. 
