MCL-1ES, a novel variant of MCL-1, associates with MCL-1L and induces mitochondrial cell death.

Myeloid cell leukemia-1 (MCL-1L) is a pro-survival member of the BCL-2 family that promotes cell survival. In this study, we identify a new splicing variant of human MCL-1 that encodes MCL-1ES (extra short). Sequence analysis indicates that this variant results from splicing within the first coding exon of MCL-1 at a non-canonical GC-AG donor-acceptor pair. The deduced sequence of MCL-1ES encodes a protein of 197 amino acids, and the PEST (proline, glutamic acid, serine, and threonine) motifs present in MCL-1L are absent. MCL-1ES interacts with MCL-1L and induces mitochondrial cell death, suggesting that alternative splicing of MCL-1 may control the fate of cells.