All life runs on 20 amino acids. These cells run key machinery on just 19

Scientists equipped Escherichia coli (example pictured) with ribosomes that lacked the amino acid isoleucine. Credit: James Cavallini/Science Photo Library All life on Earth depends on the same molecular alphabet: 20 amino acids that cells string together to make proteins. But now, scientists have reengineered bacteria to run a core part of their cellular machinery with just 19 of those amino acids — a feat akin to rewriting one act of a Shakespearean play without a common letter like “R” while keeping the text intelligible. The work is reported today in Science 1 . “It’s very exciting that it’s possible,” says Julius Fredens, a synthetic biologist at the National University of Singapore who was not involved in the research. The work offers a blueprint for engineering cells with capabilities beyond those found in nature, the authors say, while also hinting at a simpler past when early life relied on a more limited set of building blocks. Shrinking the script Researchers have long sought to rewrite the genetic code of life , both to expand what cells can do and to probe the basic rules of life. For example, scientists have streamlined DNA by removing sequence s that encode the same amino acid as other stretches. But most researchers have left the ‘canonical’ 20 amino acids untouched, because even small changes to a protein’s amino-acid sequence tend to disrupt its function. …