KMT2A and leukemia: Also, although p53, a protein usually activated to protect the cells in response to DNA damage by inducing cell cycle arrest and apoptosis (Aylon and Oren, 2007) is not often mutated in MLL-rearranged leukemia, MLL fusion proteins have been shown to suppress p53 and the p53-mediated response to DNA damage (Wiederschain et al., 2005).