In a large bowl, dissolve yeast in warm water. Add sugar and salt. Stir in flour, 1/2 cup at a time, to form a soft dough.
Turn onto a floured surface; knead until smooth and elastic, about 5 minutes (dough will be sticky). Place in a greased bowl, turning once to grease top. Cover and let rise in a warm place until doubled, about 1 hour.
Punch dough down and divide into six portions. On a lightly floured surface, roll each portion into a 14-in. rope; twist in a pretzel shape. Place on greased baking sheets. Brush with butter; sprinkle with coarse salt.
Bake at 425° for 15-20 minutes or until golden brown. Remove to wire racks. Serve warm.