Organization of toxin and antitoxin genes frompGI1 of B. thuringiensis H1.1. A) pGI1 contains a mobilization gene (mob1), a replication gene (rep1), a hypothetical transcriptional regulator (ORF5), three small cryptic ORFs (URF94, URF71, URF88) and the putative toxin-antitoxin system tasB and tasA. TasB displays similarities with the Doc toxin of bacteriophage P1. The upstream ORF, tasA, could code for the antitoxin counterpart. Putative double- and single-strand origins are also indicated. B) To assess the function of tasA and tasB, different parts of this putative toxin-antitoxin system have been amplified for cloning purposes. This figure is a scaled representation of the primers and amplimers used in cloning experiments (See Table 2 for details). Amplimer names are shown in the left column.