Edited by H. Robert Horvitz, Massachusetts Institute of Technology, Cambridge, MA, and approved November 6, 1998 (received for review August 21, 1998)
Edited by H. Robert Horvitz, Massachusetts Institute of Technology, Cambridge, MA, and approved November 6, 1998 (received for review August 21, 1998)
↵‡ P.W.F. and J.R.A. contributed equally to this work.
↵¶ To whom reprint requests should be addressed at: Cancer Center, Massachusetts General Hospital East, Building 149-7202, Charlestown, MA 02129. e-mail: hart{at}helix.mgh.harvard.edu.
This paper was submitted directly (Track II) to the Proceedings Office.
