In large bowl, sift together flour, sugar, baking powder, baking soda and salt. Cut in shortening until mixture resembles coarse meal.
In medium bowl, combine yeast with lukewarm water. Let stand until foamy, 5 to 10 minutes. Add buttermilk and stir until completely blended. Stir this liquid into dry ingredients with a fork. Gather dough into a ball.
On floured surface, knead dough until soft and smooth, adding more flour as necessary to reduce stickiness, about 5 minutes.
Roll out dough to thickness of about 1/2-inch. Using 2-inch-round cutter, stamp out biscuits and place them close together on baking sheet. Cover with kitchen towel and let rise in a warm place for 30 minutes.
Preheat oven to 400°. Bake biscuits for 10 to 15 minutes, or until nicely browned.