Vero toxin (VT1, Shiga-like toxin I)-converting phages were induced with UV light from Escherichia coli O157:H7 strain 83–1386. A non-toxigenic E. coli C600 strain, lysogenized with a toxin-converting phage (86-02), produced VT1. A phage solution was prepared from the lysogenized E. coli C600 (86-02) strain and the phage DNA was prepared.
EcoRI-fragments of the phage DNA were ligated with EcoRI-digested pBR325ΔTc and it was transformed into E. coli strain MC1061. Transformants with VT1 production commonly contained a 5.1-kb EcoRI-fragment. The restriction map of the EcoRI-fragment was prepared and it was found that a 2.1-kb BamHI-BglII fragment encoded VT1 production.