Diphtheria toxin promoter function inCorynebacterium diphtheriaeandEscherichia coli

Abstract

The expression of the diphtheria tox228 gene encoding the nontoxic, serologically related CRM228 mutant diphtheria toxin has been analyzed in Coryne-bacterium diphtheriae and Escherichia coli. The diphtheria toxin pramoter has been used to direct the expression of β-galactosidase in E.coli and the efficiency of promotion has been campared to that obtained with the lac promoter. Expression in C.diphtheriae is known to be dependent on the absence of iron, and we present for the first time direct evidence that this regulation occurs at the level of transcription. The 5′ end of toxin mRNA maps at the same position in C.diphtheriae and E.coli suggesting identical sequences to be recognized by C.diphtheriae and E. coli RNA polymerase. The diphtheria toxin promoter carries at position −34 a TTGATT sequence closely related to the E.coli −35 consensus sequence and in the −14 to −8 region a set of overlapping sequences with canplete or partial homology to the E.coli −10 consensus sequence.