Molecular and Computational Biology Program, University of Southern California, Ray Irani Hall, University Park Campus, Los Angeles, CA 90089-2910, USA. knott@usc.edu|Molecular and Computational Biology Program, University of Southern California, Ray Irani Hall, University Park Campus, Los Angeles, CA 90089-2910, USA. knott@usc.edu|Molecular and Computational Biology Program, University of Southern California, Ray Irani Hall, University Park Campus, Los Angeles, CA 90089-2910, USA. knott@usc.edu|Molecular and Computational Biology Program, University of Southern California, Ray Irani Hall, University Park Campus, Los Angeles, CA 90089-2910, USA. knott@usc.edu