Aliens sifting through the remains of a lost human civilization might puzzle over the function of a ladle. But if found in a room associated with food preparation, its purpose would become clear. Similarly, a protein relegated to mitochondria, or another specific cellular location, might have a mercifully short list of possible functions. This guilt by association, or more formally, protein localization, plays an important role in assigning function to newly identified genes and proteins. "Localization helps you predict gene function. ... If you're in the nucleolus, you're likely to be carrying out a function that is nucleolar-specific," says Charlie Boone, at the University of Toronto.