Through alternative splicing, the gene encodes both of the human proteins Bcl-xL and Bcl-xS.

Bcl-2 family members form hetero- or homodimers and act as anti- or pro-apoptotic regulators that are involved in a wide variety of cellular activities.

The proteins encoded by this gene are located at the outer mitochondrial membrane, and have been shown to regulate outer mitochondrial membrane channel (voltage-dependent anion channels (VDACs) opening.

VDACs regulate mitochondrial membrane potential, and thus controls the production of reactive oxygen species and release of cytochrome C by mitochondria, both of which are the potent inducers of cell apoptosis.

Two alternatively spliced transcript variants, which encode distinct isoforms, have been reported.