Some proteins are fluorescent—shine a light on them and they glow. And as usual nature gives us all kinds of variations including different colors. These proteins are wonderful tools for molecular biologists who use them to tag and track molecular machines at work in the cell. Now another type of fluorescent protein has beendiscovered. Not only is it from a vertebrate (the Japanese eel), but its fluorescence mechanism is different (it uses bilirubin, the four-ring molecule that we shouldn’t have too much of). As one researcher put it, “It’s totally different. There’s not anything you can point to that’s the same.” Read more