In a large bowl, dissolve yeast in water. Stir in the yolks, 3 eggs, oil, sugar, and salt. Add about 3-1/2 cups of flour to make a sticky dough. Turn dough out onto a lightly floured surface. Knead with remaining flour until smooth and elastic, about 7 minutes. Place in a well oiled bowl, and turn to oil the entire surface of the dough. Cover with a damp cloth. Place in a warm place until double in size, about 1-1/2 hours. Punch down the dough, and divide into 3 pieces. Roll each piece into a rope about 12 inches long. Braid the three strands together, and seal the ends. Place the bread on a greased cookie sheet. Beat the remaining 1 egg with a pinch of salt; brush onto bread. Let the bread rise until doubled, about 45 minutes. Preheat the oven to 375 degrees F (190 degrees C). Brush the bread with eggwash again. Bake for 40 minutes, or until golden. Cool on a wire rack.