in: Ashman K. (ed.): 'Core techniques in Biochemistry'. Heidelberg: Springer, 1997, in press.
1 EMBL, 69012 Heidelberg, Germany;
2EBI, Hinxton Hall, Hinxton, Cambridge CB10 1RQ, England
e-mail: rost@embl-heidelberg.de and schneider@embl-heidelberg.de