1. C. Baldock, J. B. Rafferty, S. E. Sedelnikova, P. J. Baker, D. W. Rice, Krebs Institute for Biomolecular Research, Department of Molecular Biology and Biotechnology, University of Sheffield, Sheffield S10 2TN, UK.
2. A. R. Stuitje, Department of Genetics, Institute of Molecular Biological Studies (IMBW), Vrije Universiteit, Biocenter Amsterdam, De Boelelaan 1087, 1081 HV Amsterdam, Netherlands.
3. A. R. Slabas, Department of Biological Sciences, University of Durham, Durham DH1 3LE, UK.
4. T. R. Hawkes, Department of Exploratory Plant Sciences, Zeneca Agrochemicals, Jealott's Hill Research Station, Bracknell, Berkshire RG12 6EY, UK.