A1 (also designated Bfl-1) is a Bcl-2 family protein that dimerizes with both Bcl-2 and Bax, and has been identified as a hematopoietic-specific, early inducible gene. Althoμgh A1 demonstrated properties similar to those of Bcl-2, its function may be more temporally regulated during myeloid differentiation and is dependent on additional growth stimuli to confer its life promoting properties. A1 is abundantly expressed in bone marrow and at low levels in other tissues. A1 expression has been correlated to stomach cancer.