[1] Swiss Fed Inst Technol, Dept Biosyst Sci & Engn, Mattenstr 26, CH-4058 Basel, Switzerland
[2] Stanford Univ, Dept Bioengn, Stanford, CA 94305 USA
[3] Univ Arizona, Dept Mol & Cell Biol 3, Tucson, AZ 85721 USA
[4] Univ Hull, Dept Chem & Biochem, Cottingham Rd, Kingston Upon Hull HU6 7RX, N Humberside, England