[1] NCI, Lab Mol Cell Biol, NIH, Bethesda, MD 20814 USA
[2] Univ Birmingham, Dept Anat, Inst Biomed Res, Birmingham B15 2TT, W Midlands, England
[3] Indiana Univ, Dept Biol, Bloomington, IN 47405 USA
[4] Indiana Univ, Ctr Genom & Bioinformat, Bloomington, IN 47405 USA
[5] MIT, Whitehead Inst, Cambridge, MA 02142 USA