Molecular Biology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA. Department of Experimental and Health Sciences, Universitat Pompeu Fabra, 08003 Barcelona, Spain. Section of Cell and Developmental Biology, Division of Biological Sciences, University of California, San Diego, La Jolla, CA, 92093-0380, USA. Molecular Biology Section, Division of Biological Sciences, University of California, San Diego, La Jolla, CA 92093, USA; San Diego Center for Systems Biology, University of California, San Diego, La Jolla, CA 92093-0380, USA; Center for Microbiome Innovation, University of California, San Diego, La Jolla, CA 92093-0380, USA. Electronic address: gsuel@ucsd.edu.