The l-asparaginases of Erwinia and E. coli have been employed for many years as effective drugs in the treatment of acute lymphoblastic leukemia and leukemia lymphosarcoma (Kristiansen et al. 1970; Kozak et al. 2002; Graham 2003), but their therapeutic response rarely occurs without some evidence of toxicity (Duval et al. 2002). The gene discussed is ASPG; the disease is acute lymphoblastic leukemia.