In a cell free system , binding of mutant __NODE__ protein ( N terminal truncation 1 639 ) and mutant __SP__ Pgc 1alpha [__NODE__] protein ( C terminal truncation 192 End ) is greater than binding of mutant __NODE__ protein ( N terminal truncation 1 639 ) and mutant __SP__ Pgc 1alpha [__NODE__] protein ( C terminal truncation 121 End ) .