MCL1 encodes a protein that helps keep cells alive (anti-apoptotic); it is frequently overexpressed in cancer. Joseph T. Opferman, PhD (Damon Runyon Fellow ‘01-‘04) and colleagues at St. Jude Children’s Research Hospital, Memphis, reported that different forms of MCL-1 reside in distinct locations in the cell’s mitochondria and exhibit separable functions. One form is anti-apoptotic, while a newly identified form that works inside the mitochondria is involved in energy production and is probably essential for tumor cell survival. This study was published in the journal Nature Cell Biology.