| A novel protein , Btf ( Bcl 2 associated transcription factor ) , that interacts with E1B 19K as well as with the antiapoptotic family members Bcl 2 and Bcl xL but not with the proapoptotic protein Bax was identified . btf is a widely expressed gene that encodes a protein with homology to the basic zipper ( bZip ) and Myb DNA binding domains . ^^^ E1B 19K , Bcl 2 , and Bcl xL sequester Btf in the cytoplasm and block its transcriptional repression activity . ^^^ |