The present invention provides polynucleotide sequences (bbp) encoding a Bak Binding Protein (BBP) and fragments thereof that bind to Bak. The invention also provides a BBP which binds to Bak. The invention also provides recombinant host cells containing polynucleotides encoding BBP. The invention further provides antibodies that specifically bind to BBP. The invention further provides methods for detecting agents such as drugs that alter the binding of a BBP with a Bak protein. The invention further provides methods for detecting the presence of bbp or BBP in a biological sample, and further provides methods for modulating the levels of BBP in a cell. This invention additionally encompasses novel peptides, designated the "BBP Binding Domains" and the respective nucleotides, designated "bbpbd-1" and "bbpbd-2" which are involved in the interaction between Bak and BBP.