RESUMO
In a protein-synthesizing system extracted from E. coli, purified DNA from corynephages betac(tox+) and beta45c was used to direct the in vitro synthesis of diphtheria toxin and of the related nontoxic protein, CRM45, as well as of other beta-phage proteins. When betac(tox+)-DNA or betac-DNA was added to a similar system extracted from the nonlysogenic Corynebacterium diphtheriae strain, C7(s)(-)(tox-), neither toxin nor the CRM45 protein was produced, although other beta-phage proteins were synthesized in amounts equivalent to those produced in the E. coli system from the same amount of beta-phage DNA. Preliminary experiments suggest that both toxinogenic and nontoxinogenic strains of the diphtheria bacillus contain a factor that specificially blocks expression of the tox gene. Synthesis of toxin and the CRM45 protein in the E. coli system could not be inhibited by relatively high concentrations of inorganic iron, but could be inhibited by extracts from the C7(s)(-)(tox-) strain of C. diphtheriae.
