Mcl-1 (Myeloid cell leukemia-1) is a 37 kDa Bcl-2-related protein with an apparent molecular weight of 43 kDa on SDS-PAGE. Mcl-1 was identified as an early-induction gene that increased in expression during the differentiation of human myeloblastic leukemia cell ML-1, or exposure to different DNA damaging agents. The level of Mcl-1 is decreased in peripheral B lymphocytes undergoing apoptosis following treatment with apoptotic stimuli such as TGF-β1 and forskolin. Expression of Mcl-1 is able to delay apoptosis induced by over-expression of c-myc in CHO 5AHSmyc cells. In hematopoietic FDC-P1 cells, Mcl-1 interacts with another Bcl-2-related protein, Bax, and prolongs cell viability after treatment with different apoptotic reagents.