At any given time, a number of ribosomes (grey ovals) will be attached to messenger RNA molecules at different positions. Ribosomal profiling is a technique that can help to locate ribosomes on the mRNA they are translating at the scale of the genome. First, each ribosome (and the region of mRNA it is attached to) is isolated. These segments are then treated with nucleases, releasing the RNA sequences the ribosomes were bound to. These are then purified and sequenced. During efficient termination (left), most of the ribosomes are between the start codon (green) and the stop codon (red), with the majority accumulating at the stop codon (graph on the bottom left), where translation stops. During inefficient termination (right), for example under the influence of small molecules such as G418, ribosomes can ‘readthrough’ the termination codon and carry on translating downstream (graph on the bottom right).