Division of Biochemistry and Molecular Biology, School of Biological Sciences, University of Southampton, Bassett Crescent East, Southampton SO16 7PX, , UK1
Department of Biology, Sir Alexander Fleming Building, Imperial College of Science, Technology and Medicine, London SW7 2AZ, , UK2
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, PA 16802-4500, , USA3
Author for correspondence: David J. Studholme. Tel: +44 23 8059 4324. Fax: +44 23 8059 4459. e-mail: djs{at}soton.ac.uk