ABSTRACT
The application of current molecular biological techniques has permitted dissection and manipulation of the gene, thus permitting a detailed analysis of the protein and a way to wield the extreme potency of the toxin for targeting to discrete cell populations. In 1888, the bacterium Corynebacterium diphtheriae was shown to secrete a protein toxin which contributed to the pathogenicity of diphtheria. It took over 65 years to demonstrate an association between bacteria producing diphtheria toxin and lysogenization by bacteriophage. The lack of spontaneous conversion of nontoxinogenic strains to toxinogenicity in the absence of infection by bacteriophage, and the rapid appearance of toxinogenic cells following infection, argued against the selection of a “mutant” population in favor of an induced change associated with the phage. In order to clone the diphtheria toxin gene, phage genome restriction fragments bearing tox were identified so that the smallest fragment containing the entire diphtheria toxin gene could be cloned with a minimum amount of extraneous phage DNA.
