The amino-acid sequence of two non-toxic mutants of diphtheria toxin: CRM45 and CRM197

Nucleic Acids Res. 1984 May 25;12(10):4063-9. doi: 10.1093/nar/12.10.4063.


The amino-acid sequences of two diphtheria toxin-related, non-toxic proteins, CRM45 and CRM197 , were deduced from the complete sequence of their genes: tox 45 and tox 197. CRM45 lacks the last 149 C-terminal amino-acid residues, but is otherwise identical to diphtheria toxin: a single C----T transition introduces an "ochre" (TAA) termination signal in tox 45, after the codon for threonine-386. A single G----A transition was also found in tox 197, leading to the substitution of glycine-52, present in the wild-type toxin, with glutamic acid in CRM197 . This aminoacid change is responsible for the loss of the NAD:EF2 ADP-ribosyltransferase activity in CRM197 , due most probably to an alteration of the NAD+ binding site.

MeSH terms

  • Amino Acid Sequence
  • Bacterial Proteins / genetics*
  • Base Sequence
  • Corynebacterium diphtheriae / genetics
  • Cross Reactions
  • Diphtheria Toxin / genetics*
  • Genes*
  • Genes, Bacterial*
  • Mutation*


  • Bacterial Proteins
  • CRM45 fragment of diphtheria toxin
  • Diphtheria Toxin
  • CRM197 (non-toxic variant of diphtheria toxin)