1. Division Molecular Biology of the Cell I, (D.H., J.R.P., G.S.), 69120 Heidelberg, Germany
2. Division Cellular and Molecular Pathology, (S.K., H.-J.G.), 69120 Heidelberg, Germanyx
3. German Cancer Research Center, and Heidelberg University Biochemistry Center, (B.B., F.W.) 69120 Heidelberg, Germany