The temperate B. subtilis phage ϕ105 genome contains at least two distinct regions encoding superinfection immunity

Two different PstI fragments of temperate phage ϕ105 DNA are shown to confer superinfection immunity upon Bacillus subtilis when inserted into the multicopy cloning vector pE194 cop-6. The 2.3 kb PstI fragment I is located almost entirely within EcoRI fragment F and encompasses a region previously known to encode a repressor. The other fragment, PstI-E (4.3 kb) maps inside the EcoRI-B fragment, and allows an explanation of the clear-plaque phenotype of the deletion mutant ϕ105DII:6c. The two regions can be distinguished functionally, since only the PstI fragment I product interacts with a specific ϕ105 promoter-operator site

The use of the Ti plasmid as a vector for the introduction of foreign DNA into plants

Agrobacterium tumefaciens is a Gram-negative bacterium with the unique capacity to induce neoplasmic transformations in dicotyledonous plants. Recently, both the mechanism and the biological significance of this transformation have been elucidated. Agrobacterium tumefaciens strains contain a large extrachromosomal DNA plasmid (the Ti-plasmid). This Ti-plasmid is responsible for the oncogenic properties of Agrobacterium strains. A particular segment of the Ti-plasmid, containing information determining the tumorous growth pattern and the synthesis of so-called "opines", e.g. "octopine" (N²-(D-1-carboxyethyl)-L-arginine) and "nopaline" (N²-(1,3-dicarboxypropyl)-L-arginine), is transferred and stably maintained and expressed in the transformed plant cells by bacterial plasmid DNA so that the transformed plant cell will produce and secrete into the medium amino acid derivatives (the opines) that Ti-plasmid carrying agrobacteria can selectively use as carbon and nitrogen sources. By in vivo genetic manipulations, we have recently been able to introduce a bacterial antibiotic resistance transposon, Tn7, in the Ti-DNA segment that is transferable to plant cells. In this way we hope to demonstrate that the Ti-plasmid can be used as a general vector for introducing "foreign" DNA into plants