<prompt> All are true regarding diphtheria toxin except ?Toxin blocks elongation of proteinBeta lysogenic strain produces toxinIron is critical for toxin productionToxin is necessary for local wound production  <response>: Option 4 Corynebacteriam diphtheriae does not need to be toxigenic to establish localized infection. Option 1, 2, 3 Mechanism of Action of diphtheria toxin Has 2 fragments: Fragment A active unit Fragment A is internalized into the host cells and then causes- ADP ribosylation of elongation factor 2EF2 - inhibition of EF2- irreversible inhibition of translation step of protein synthesis- cell death. Fragment B binding unit Binds to the host cell receptors such as epidermal growth factor Helps in entry of fragment A. Toxin Production is dependent on: Phage coded: DT is coded by b corynophage carrying tox gene. Iron concentration: Toxin production depends on optimum iron concentration 0.1 mgliter. DT repressor gene DtxR is an iron dependent negative regulator of DT production and iron uptake in C.diphtheriae. 