In a cell free system , binding of __SP__ G __NODE__ protein and mutant __SP__ __NODE__ [__NODE___alpha] protein ( S442A S532A with its phosphorylation site mutated N terminal truncation 1 279 ) is greater than binding of __SP__ G __NODE__ protein and phosphorylated ( S442 S532 ) mutant __SP__ __NODE__ [__NODE___alpha] protein ( N terminal truncation 1 279 ) .