Description
N-terminal GST-tagged recombinant, human JAK1 amino acids 866-end. Activated in vitro by auto-phosphorylation. Janus kinase 1 (JAK1), is a member of a new class of protein-tyrosine kinases (PTK) characterized by the presence of a second phosphotransferase-related domain immediately N-terminal to the PTK domain. The second phosphotransferase domain bears all the hallmarks of a protein kinase, although its structure differs significantly from that of the PTK and threonine/serine kinase family members. JAK1 is a large, widely expressed membrane-associated phosphoprotein. JAK1 is involved in the interferon-α/beta and -γ signal transduction pathways. The reciprocal interdependence between JAK1 and TYK2 activities in the interferon-α pathway, and between JAK1 and JAK2 in the interferon-γ pathway, may reflect a requirement for these kinases in the correct assembly of interferon receptor complexes. These kinases couple cytokine ligand binding to tyrosine phosphorylation of various known signaling proteins and of a unique family of transcription factors termed the signal transducers and activators of transcription, or STATs