An oncogene with a split personality

Find a tumor in a human or rodent, and the chances are that lurking within it will be an activated ras gene. The cancer-police have been trailing it for the better part of two decades and the file of incriminating evidence is large. Now findings show that ras genes are not all bad, though there is a long way to go before their complex nature is fully understood.

Ras genes (H, K and N ras) code for small GTP-binding switch proteins, which are part of a communications trail that relays signals from receptors on the cell surface to the interior. Mutations can leave these Ras proteins in a permanently active state and so in the absence of any external signal they constantly promote cell proliferation.

Initial observations in the late 1980s and early 1990s suggested that mutated ras genes were dominant, because they were expressed even when the normal alleles...