In a cell free system , binding of heterodimer consisting of __SP__ __NODE__ and of __SP__ __NODE__ and PPRE 1 from __SP__ __NODE__ gene is greater than binding of heterodimer consisting of __SP__ __NODE__ and of __SP__ __NODE__ and PPRE 1 from mutant __SP__ __NODE__ gene ( T 673G with its PPRE 1 mutated ) .