In a mixing bowl, dissolve yeast in water. Add sugar, 1/4 cup butter, shortening, eggs, salt and 2 cups flour; beat until smooth. Add enough of the remaining flour to form a soft dough. Knead on floured surface until smooth and elastic, about 6 to 8 minutes. Place in greased bowl; turn once to grease top. Cover and let rise in warm place until double in size, about 1-1/2 hours.
Punch the dough down; divide in half. Roll each portion into a 12 inch circle. Melt remaining butter; brush over dough. Cut each circle into 12 wedges. Roll up wedges form the wide end and curve to form crescents. Place with point down 2 inches apart on greased baking sheets. Cover and let rise in warm place until crescents double in size, about 45 minutes. Bake at 375 °F for 8 to 10 minutes or until golden brown. Brush with butter if desired.