Regulation of ribosomal DNA amplification by the TOR pathway

We tend to think of our genome as an unchanging store of information; however, recent evidence suggests that genomes vary between different cells in the same organism. How these differences arise and what effects they have remain unknown, but clearly our genome can change. In a single-celled organism, genome changes occur at random, and advantageous changes slowly propagate by natural selection. However, it is known that the DNA encoding ribosomes can change simultaneously in a whole population. Here we show that signaling pathways that sense environmental nutrients control genome change at the ribosomal DNA. This demonstrates that not all genome changes occur at random and that cells possess specific mechanisms to optimize their genome in response to the environment.