Preheat oven to 400°F (200°C).
In a small bowl, dissolve yeast in warm water and let stand for 5 minutes.
In a large mixing bowl, combine flour, baking powder, baking soda, salt, and sugar.
Cut in shortening until mixture resembles coarse crumbs.
Stir in yeast mixture and buttermilk until just combined.
Turn dough out onto a floured surface and knead lightly.
Roll dough to ½ inch thickness and cut with a biscuit cutter.
Place biscuits on a greased baking sheet and let rise for 1 hour.
Bake for 12-15 minutes or until golden brown.
Brush with melted butter and serve warm.