Heat oven to 350 degrees F. Coat 12-cup bundt pan with nonstick cooking spray.
In large bowl, mix cake mix, 1 cup of the sour cream, eggs, vegetable oil and water on low speed until moistened. Scrape down sides of bowl. Increase speed to high and beat 2 minutes. Add poppy seeds and beat until just evenly distributed. Pour batter into prepared bundt pan.
Bake in 350 degree F oven for 45 to 50 minutes or until toothpick inserted in center comes out clean. Cool on wire rack 20 minutes. Run a small knife or spatula around edge and center of bundt to loosen cake. Turn out onto wire rack and cool completely.
Place frosting in medium-size bowl and microwave on high 6 to 7 seconds. Whisk in the remaining 1/4 cup of sour cream. Pour over cooled cake. Refrigerate for 1 hour to set frosting. Makes 12 servings.