[1] Nat Hist Museum, Dept Zool, London SW7 5BD, England
[2] Univ Edinburgh, Inst Cell Anim & Populat Biol, Edinburgh, Midlothian, Scotland
[3] Inst Oswaldo Cruz, Dept Biochem & Mol Biol, BR-20001 Rio De Janeiro, Brazil
[4] New England Biolabs Inc, Beverly, MA 01915 USA
[5] Univ London Imperial Coll Sci Technol & Med, Dept Biochem, London, England
[6] Univ Cambridge, Dept Pathol, Cambridge CB2 1TN, England