In a bowl combine well the cornmeal, the flour, the sugar, the baking powder, the baking soda, and the salt, add margarine and blend the mixture until it resembles coarse meal. Stir in the buttermilk and the egg and stir the batter until it resembles coarse meal. Bake the bread in a grease 8 inch square baking pan. In 425' F. oven for 25 minutes, or until the top is golden and a skewer comes out clean. Let the corn bread cool in the pan for 5 minutes.