Boldface terms within a definition are also defined in this glossary.

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JAK kinase A class of protein tyrosine kinases that are bound to the cytosolic domain of cytokine receptors and are activated following cytokine binding.

JAK/STAT pathway A cell signaling pathway used by several cytokine receptors, in which a JAK kinase phosphorylates a receptor-bound STAT transcription factor, inducing its movement into the nucleus, where it activates transcription.