[1] Univ Colorado, Dept Mol Cellular & Dev Biol, Boulder, CO 80303 USA
[2] Univ Colorado, Dept Chem & Biol Engn, Boulder, CO 80303 USA
[3] Univ Colorado, Dept Chem & Biochem, Boulder, CO 80303 USA
[4] Lawrence Berkeley Natl Lab, Phys Biosci Div, Berkeley, CA 94720 USA
[5] Dept Bioengn, Berkeley, CA 94720 USA