Center for Biomolecular Science and Engineering, University of California Santa Cruz, Santa Cruz, California, USA. jsp@soe.ucsc.edu|Center for Biomolecular Science and Engineering, University of California Santa Cruz, Santa Cruz, California, USA. jsp@soe.ucsc.edu|Center for Biomolecular Science and Engineering, University of California Santa Cruz, Santa Cruz, California, USA. jsp@soe.ucsc.edu|Center for Biomolecular Science and Engineering, University of California Santa Cruz, Santa Cruz, California, USA. jsp@soe.ucsc.edu|Center for Biomolecular Science and Engineering, University of California Santa Cruz, Santa Cruz, California, USA. jsp@soe.ucsc.edu|Center for Biomolecular Science and Engineering, University of California Santa Cruz, Santa Cruz, California, USA. jsp@soe.ucsc.edu|Center for Biomolecular Science and Engineering, University of California Santa Cruz, Santa Cruz, California, USA. jsp@soe.ucsc.edu|Center for Biomolecular Science and Engineering, University of California Santa Cruz, Santa Cruz, California, USA. jsp@soe.ucsc.edu|Center for Biomolecular Science and Engineering, University of California Santa Cruz, Santa Cruz, California, USA. jsp@soe.ucsc.edu