Add the starter, yogurt, sour cream, butter, eggs, sugar, salt, vanilla, and flour to the pan of a bread machine. Program to the dough cycle. Allow the dough cycle to complete itself.
Remove dough from bread machine to floured surface. Divide in half; wrap one half in plastic wrap for another use.
Roll into 12 x 18-inch rectangle.
Melt 4 Tablespoons butter; brush onto dough.
Combine ½ cup granulated sugar and cinnamon in small bowl. Sprinkle on dough, leaving 1-inch border on all sides.
Starting with one long end, roll into a log. Pinch dough to seal. With sharp knife, cut in half, length-wise, leaving I-inch on end uncut. Braid the halves together, keeping the open layers exposed. Form the dough into a ring. Moisten the ends of the dough with a little water; pinch the two ends together to seal. Place a large greased can in the center to maintain a nice circle in the center. Transfer to parchment lined baking sheet. Cover with a clean dish towel, and let rise in a warm place until doubled in size, about 30 minutes.
Preheat oven to 350° F. Bake in preheated oven until the top is golden brown, about 25 minutes.
Remove from oven; brush top with 1 Tablespoon melted unsalted butter. Transfer to wire rack; cool completely.