Preheat oven to 375 degrees F (190 degrees C). Lightly grease a large baking sheet.
In a large bowl, mix together flour, sugar, baking soda, baking powder, salt and margarine. Stir in 1 cup of buttermilk and egg. Turn dough out onto a lightly floured surface and knead slightly. Form dough into a round and place on prepared baking sheet. In a small bowl, combine melted butter with 1/4 cup buttermilk; brush loaf with this mixture. Use a sharp knife to cut an 'X' into the top of the loaf.
Bake in preheated oven for 45 to 50 minutes, or until a toothpick inserted into the center of the loaf comes out clean, about 30 to 50 minutes. You may continue to brush the loaf with the butter mixture while it bakes.