1. T. Nosaka, W. E. Thierfelder, B. A. Witthuhn, J. N. Ihle, Department of Biochemistry, St. Jude Children's Research Hospital, 332 North Lauderdale, Memphis, TN 38105, USA.
2. J. M. A. van Deursen and G. C. Grosveld, Department of Genetics, St. Jude Children's Research Hospital, 332 North Lauderdale, Memphis, TN 38105, USA.
3. R. A. Tripp, A. P. McMickle, P. C. Doherty, Department of Immunology, St. Jude Children's Research Hospital, 332 North Lauderdale, Memphis, TN 38105, USA.