Mcl-1 (Myeloid cell leukemia-1) is a member of the bcl-2 family. The carboxy terminal of Mcl-1 and bcl-2 share significant sequence homology. Expression of Mcl-1 is increased upon exposure of ML-1 cells to various types of DNA damaging agents (e.g. ionizing radiation, ultraviolet radiation, and alkylating drugs) along with increases in GADD45 and Bax and a decrease in bcl-2. Enhanced expression of Mcl-1, prominently associated with mitochondria, complements the continued expression of bcl-2 in ML-1 cells undergoing differentiation. Like bcl-2, Mcl-1 has the capacity to promote cell viability under conditions that otherwise cause apoptosis.