Enables several functions, including CD4 receptor binding activity; protein antigen binding activity; and protein phosphatase binding activity. Involved in release of sequestered calcium ion into cytosol. Acts upstream of or within several processes, including positive regulation of macromolecule metabolic process; protein phosphorylation; and regulation of T cell differentiation. Located in cell-cell junction. Colocalizes with plasma membrane. Is expressed in several structures, including 2-cell stage embryo; nervous system; neural ectoderm; sensory organ; and thymus primordium. Human ortholog(s) of this gene implicated in immunodeficiency 22. Orthologous to human LCK (LCK proto-oncogene, Src family tyrosine kinase). [provided by Alliance of Genome Resources, Apr 2022]