• A unique reaction of eEF2 is its susceptibility todiphtheria toxin. The toxin uses NAD(nicotinamide adenine dinucleotide) as a cofactorto transfer an ADPR moiety (adenosinediphosphate ribosyl) on to the eEF2. The ADPReEF2conjugate is inactive in protein synthesis.The substrate for the attachment is an unusualamino acid, produced by modifying a histidine; itis common to the eEF2 of many species.
TerminationA stop codon (Termination codon) is one of three triplets (UAG, UAA, UGA)that causes protein synthesis to terminate. They are also known historically asnonsense codons. The UAA codon is called ochre, and the UAA codon is calledamber, after the names of the nonsense mutations by which they wereoriginally identified.The amber codon is the triplet UAG, one of the three termination codons thatend protein synthesis.The ochre codon is the triplet UAA, one of the three termination codons thatend protein synthesis.The opal codon is the triplet UGA, one of the three termination codons that endprotein synthesis. It has evolved to code for an amino acid in a small number oforganisms or organelles.Missense mutations change a single codon so as to cause the replacement ofone amino acid by another in a protein sequence.Premature termination describes the termination of protein or of RNAsynthesis before the chain has been completed. In protein synthesis it can becaused by mutations that create termination codons within the coding region. InRNA synthesis it is caused by various events that act on RNA polymerase.A nonsense mutation is any change in DNA that replaces a codon specifyingan amino acid with a translation-termination codon (UAG, UGA, or UAA).