Karen Strahan, Andrew Preece and Kenth Gustafsson

Division of Cell & Molecular Biology, Institute of Child Health, University of London, 30 Guilford St., London WC1N 1EH, UK

Received 06/21/96; Accepted 07/02/96; On-line 07/08/96

We are grateful to Prof. J. W. Fabre, Dr. J. Greenstein, and Dr. M. Rosa for helpful discussions and for critical reading of the manuscript. We wish to thank Prof. D. H. Sachs, Dr. M. Baetscher, and Dr. Y. Xu for stimulating discussions, as well as Dr. D. Joziasse for helpful comments. This work was partially supported by the British Heart Foundation and Bio-Transplant Inc.