CTPS1 and leukemia: CTP is synthesized from UTP by CTP synthase, which is the rate-limiting step of de novo CTP biosynthesis and probably a practical target just as in the treatment of leukemia (Verschuur et al., 1998) and parasitic infestations (Hofer et al., 2001; Fijolek et al., 2007; Tamborini et al., 2012).