1. Department of Biochemistry, Albert Einstein College of Medicine, Bronx, NY 10461, U.S.A.
2. Department of Anatomy and Cell Biology, Columbia University College of Physicians and Surgeons, New York, NY 10032, U.S.A.
3. Department of Medicine, Columbia University College of Physicians and Surgeons, New York, NY 10032, U.S.A.
4. Department of Medicine, Marion Bessin Liver Research Center, Albert Einstein College of Medicine, Bronx, NY 10461, U.S.A.