The affinity of binding of __SP__ __NODE__ protein in a system of purified components and soluble mutant __SP__ __NODE__ A protein ( deletion 602 703 with its __NODE__ type III domain 2 deleted and with its carboxy terminal domain and its CR domain and its __NODE__ type III domain 1 and its linker domain ( aa sequence NPSVPLDP ) and its loop domain 1 2 retained ) in a system of purified components is the same as the affinity of binding of __SP__ __NODE__ protein in a cell fraction from B lymphocytes and mutant __SP__ __NODE__ protein ( C terminal truncation ) in a cell fraction from B lymphocytes .