Institute for Cellular and Molecular Biology and Department of Mathematics, University of Texas at Austin, Austin, Texas 78712, USA. jcyao@mail.utexas.edu|Institute for Cellular and Molecular Biology and Department of Mathematics, University of Texas at Austin, Austin, Texas 78712, USA. jcyao@mail.utexas.edu|Institute for Cellular and Molecular Biology and Department of Mathematics, University of Texas at Austin, Austin, Texas 78712, USA. jcyao@mail.utexas.edu|Institute for Cellular and Molecular Biology and Department of Mathematics, University of Texas at Austin, Austin, Texas 78712, USA. jcyao@mail.utexas.edu|Institute for Cellular and Molecular Biology and Department of Mathematics, University of Texas at Austin, Austin, Texas 78712, USA. jcyao@mail.utexas.edu|Institute for Cellular and Molecular Biology and Department of Mathematics, University of Texas at Austin, Austin, Texas 78712, USA. jcyao@mail.utexas.edu