WNK3 (WNK lysine deficient protein kinase 3) belongs to the serine/threonine protein kinase family. It lacks the almost invariant catalytic lysine in subdomain II, which is important for binding ATP in the catalytic site. A conserved lysine in subdomain I is thought to provide this function. WNK3 activates Na-(K)-Cl cotransporters by increasing their phosphorylation and appears to be a crucial component of the kinase/phosphatase signaling pathway that coordinately regulates the Cl– influx and efflux branches of the SLC12A cotransporter family.