A stress-induced hidden secret of the genetic code in Escherichia coli

Different codons that encode the same amino acids are known as synonymous codons. They appear in different frequencies, also designated as codon usage bias, that vary from species to species and have functional implications. Here I summarise and discuss our recent findings of a novel stress-mediated bias in the reading of the genetic code in E.coli. Under stress, the toxin MazF having endoribonucleolytic activity of cleaving ACA sites is induced. Thereby, generating a unique stress translation machinery (STM) composed of processed or leaderless mRNAs and defective ribosomes. Through the STM system, the amino acid threonine is encoded mostly by its synonymous codons ACC, ACU, or ACG, instead of by ACA.