In a cell free system , binding of mutant __NODE__ protein ( N terminal truncation 1 639 ) and mutant __SP__ __NODE__ protein ( C terminal truncation 451 End with its AF 2 domain deleted ) is greater than binding of mutant __NODE__ protein ( N terminal truncation 1 639 ) and mutant __SP__ __NODE__ protein ( C terminal truncation 289 End with its AF 2 domain deleted and with its ligand binding domain mutated ) .