Preheat oven to 350 degrees F. Beat cake mix, butter and 1 egg in large bowl with mixer until crumbly. Stir in saltine crumbs. Set aside 2 cups of crumb mixture. Press remaining crumb mixture on bottom of greased 13x9-inch baking pan.
Bake 15 to 20 minutes or until lightly golden. Beat 3 egg yolks, condensed milk and ReaLemon(R) with mixer or wire whisk. Spread over prepared crust. Top with reserved crumb mixture. Bake 25 minutes longer or until set and top is golden. Cool.
Refrigerate within 2 hours. Cut into bars. Store leftovers covered in refrigerator.