In a small mixing bowl, COMBINE yeast and warm water; let STAND until bubbly, about five minutes; ADD buttermilk; SET aside.

In a large mixing bowl, COMBINE dry ingredients--flour, sugar, baking powder, soda, salt.

CUT in shortening until mixture resembles coarse meal.

ADD buttermilk mixture, MIXING with a fork until dry ingredients are moistened.

TURN dough onto a floured surface; KNEAD lightly three or four times.

ROLL dough to 1/2-inch thickness; CUT with a 2 3/4-inch biscuit cutter.

PLACE on lightly greased baking sheets; COVER; let RISE one hour.

BAKE at 425 F until golden brown, about eight to ten minutes