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2. M. E. McCurrach and S. W. Lowe, Cold Spring Harbor Laboratories, 1 Bungtown Road, Cold Spring Harbor, NY 11724, USA.
3. H.-B. Shu and D. V. Goeddel, Tularik, 2 Corporate Drive, South San Francisco, CA 94080, USA.
4. K. Mitchell and W. S. El-Deiry, Howard Hughes Medical Institute, University of Pennsylvania School of Medicine CRB 437A, Philadelphia, PA 19104, USA.