ananyo writes with an excerpt from a Nature news release: "By bringing long-dead proteins back to life, researchers have worked out the process by which evolution added a component to a cellular machine. ... In a paper published in Nature, researchers recreated an 'ancestral' version of a cellular machine called the V-ATPase proton pump, which channels protons across membranes and is vital for keeping cell compartments at the right acidity. Part of this machine is a ring of six proteins that threads through the membrane. Animals and most other eukaryotes have a ring composed of two types of protein component; fungi are alone in having a ring with three. The researchers used computational methods to work backwards and find the most likely sequences of these proteins hundreds of millions of years ago. The team inserted the DNA into yeast and found that just two mutations can turn the simple 2-protein ring into the more complex 3-protein ring."