[1] Univ Colorado, Sch Med, Dept Cellular & Dev Biol, Hlth Sci Ctr, Denver, CO 80262 USA
[2] Univ Glasgow, Fac Biomed & Life Sci, Henry Wellcome Lab Cell Biol, Div Biochem & Mol Biol, Glasgow G12 8QQ, Lanark, Scotland
[3] Univ Dundee, Div Gene Regulat & Express, Wellcome Trust Bioctr, Dundee DD1 5EH, Scotland
[4] Univ Leicester, Dept Biochem, Leicester LE1 7RH, Leics, England
[5] Genentech Inc, San Francisco, CA 94080 USA