Enables protein tyrosine kinase activity. Involved in negative regulation of cytokine production. Acts upstream of or within several processes, including B cell affinity maturation; I-kappaB kinase/NF-kappaB signaling; and negative regulation of B cell proliferation. Located in cytoplasmic vesicle and nucleus. Is expressed in liver left lobe; liver right lobe; spleen; and thymus primordium. Used to study X-linked agammaglobulinemia. Human ortholog(s) of this gene implicated in agammaglobulinemia (multiple); isolated growth hormone deficiency type III; and lymphoma (multiple). Orthologous to human BTK (Bruton tyrosine kinase). [provided by Alliance of Genome Resources, Apr 2022]