1. J. Craig Venter Institute, La Jolla, CA 92037, USA.
2. National Center for Microscopy and Imaging Research, University of California–San Diego, La Jolla, CA 92037, USA.
3. Synthetic Genomics, La Jolla, CA 92037, USA.
4. National Institute of Standards and Technology, Gaithersburg, MD 20899, USA.