NOTCH1 and leukemia: As the ICN allele used above models the rare t(7:9) translocation and encodes a potent transcriptional transactivator [16], we tested the Notch1ΔEGFΔLNRΔP construct (defined here as N1ΔEGF), which better models the leukemia-associated NOTCH1 mutations disabling the negative regulatory region and PEST domain commonly seen in patients, and exhibits a weaker transcriptional activity than ICN [28].