proto-oncogene

A proto-oncogene is a perfectly normal, useful gene that has a dangerous potential. Picture a brake-free accelerator pedal that works fine while you control it; the proto-oncogene is the healthy pedal, and only when it gets jammed in the down position does it become a problem. In its everyday role it helps the cell grow and divide at the right times.

Proto-oncogenes encode proteins involved in growth signals, cell-cycle progression, and survival, such as growth-factor receptors, signaling enzymes, and transcription factors. They are essential for normal development and tissue repair. The word proto- (meaning earlier or original) marks them as the precursors that can later become cancer-driving genes.

When a proto-oncogene is changed by mutation, duplication, or chromosomal rearrangement so that it becomes overactive, it turns into an oncogene. Importantly, the starting gene is not defective; it is the alteration that flips a normal growth-control gene into a growth-driving one.