[1] UNIV CAMERINO, LAB MOLEC BIOL, CAMERINO, ITALY
[2] UNIV ROME, CTR MOLEC BIOL, INST BIOCHEM, CONSIGLIO NAZL RICERCHE, ROME, ITALY
[3] UNIV ROME, CTR MOLEC BIOL, INST CHEM, CONSIGLIO NAZL RICERCHE, ROME, ITALY
[4] UNIV E ANGLIA, SCH BIOL SCI, NORWICH NOR 88C, ENGLAND