In a large bowl combine flour, sugar, baking powder, and salt. With pastry blender or two knives, cut in shortening until mixture resembles course crumbs, set aside.
Place warm water in warm bowl. Sprinkle in yeast, stir until dissolved. Add yeast mixture and warm buttermilk to dry ingredients, blend well.
Remove dough to floured surface. Knead dough 10 to 15 times, form into ball. Roll dough to 3/4 inch thickness. Cut into 2-1/2 inch biscuits. Cover and let rise until doubled in bulk, about 30 to 45 minutes.
Bake at 400 degrees F (205 degrees C) for 15 minutes or until done.