Predicted to enable growth hormone receptor binding activity and non-membrane spanning protein tyrosine kinase activity. Acts upstream of or within T cell differentiation in thymus. Predicted to be located in cytoskeleton; endomembrane system; and membrane. Predicted to be active in cytosol. Is expressed in cranial ganglion; otic vesicle; somite; and vasculature. Human ortholog(s) of this gene implicated in T-cell acute lymphoblastic leukemia; carcinoma (multiple); gastrointestinal system cancer (multiple); and reproductive organ cancer (multiple). Orthologous to human JAK1 (Janus kinase 1).