Further supporting a critical role for the MCM2–7 and the pre-RC in Ewing sarcoma tumors, the Dbf4-dependent Cdc7 kinase (DDK), which initiates replisome assembly by phosphorylating the N-terminal tails of Mcm2, Mcm4, and Mcm6, was recently identified as a target in Ewing sarcoma tumors (3, 26, 27). Here, MCM4 is linked to Ewing sarcoma.