FIGURE 1. Accuracy in gene expression.

Transfer of information from the DNA sequence of a gene to the corresponding amino-acid sequence of a protein requires transcription of the sequence into messenger RNA, then translation of that RNA into an amino-acid sequence at ribosomes, through the agency of amino-acid-specific transfer RNAs. These steps are all prone to error (typical rates are shown in red). The inset shows the aminoacylation of tRNA, in which an amino acid is paired with a tRNA by the enzyme aminoacyl-tRNA synthetase (aaRS). It is a failure of quality control at this stage that Lee et al.² show causes neurodegeneration in 'sticky mice'. Once synthesized, a protein usually becomes functional. In some cases, however, misfolding occurs. Most misfolded proteins are degraded by the cell — but some form insoluble aggregates that, as in the sticky mouse, can lead to disease.