J. S. Bader is in the Department of Biomedical Engineering and High-Throughput Biology Center
Johns Hopkins University, 3400 North Charles Street, Baltimore, MD 21215, USA. E-mail: <span class="em-link"><span class="em-addr">joel.bader{at}jhu.edu</span></span>;J. Chant is at Genentech, Inc., 1 DNA Way, South San Francisco, CA 94080, USA. E-mail: <span class="em-link"><span class="em-addr">jchant{at}gene.com</span></span>