The BAK1 gene, with 7748 bases in length, and contains 6 exons. The first exon is non-coding, and most of the largest, final exon is untranslated.

The BAK1 gene transcribes a 211 aa protein Bak. A possible 101 aa splice variant, called BAK-like, contains BH1, BH2 and TM domains, but no BH3 domain, with a 2.4 kb transcript of BAK-like detected in most human tissues and exhibiting pro-apoptotic activity. Two other human BAK1 mRNA variants are present in GenBak but may not be expressed: the BakM variant would be 190 aa and lack 21 amino acids in the linker region between alpha-helices 1 and 2; another would be 153 aa with the stop codon upstream of a splice junction and therefore predicted to be subject to nonsense-mediated mRNA decay. However in mice, a similar 151 aa N-Bak that contains only the BH3 domain is reportedly expressed in neurons.

There are two pseudogenes: Bak2 (chromosome 20) and Bak3 (chromosome 11).

The BAK1 gene encodes for a 23409 Da protein, named Bak. The Bak cDNA was isolated by three groups by virtue of its protein product interacting with the adenovirus E1B 19K protein, or its homology to the BH1 and BH2 domains of Bcl-2. The BH3 domain of Bak is essential for its binding to a hydrophobic surface groove on the prosurvival proteins Bcl-xL and Mcl-1. The Bak BH3 domain is also important for binding to a similar hydrophobic groove in another activated Bak molecule to form Bak oligomers and the formation of pores.

BAK1 mRNA is expressed widely in different tissues as an approximately 2.4 kb transcript. Highest mRNA levels are in the heart and skeletal muscle.

The Bak protein is inserted in the mitochondrial outer membrane in healthy cells, while its close homologue Bax translocates to mitochondria after an apoptotic stimulus. A small proportion of Bak has also been detected at the endoplasmic reticulum membrane.

Bak (or Bax) is required to form pores in the mitochondrial outer membrane during apoptotic cell death. The killing activity of Bak is regulated by other members of the Bcl-2 family. For example, certain BH3-only proteins (Bim and Bid) are reported to directly bind Bak to convert it into the activated conformation, while the prosurvival proteins (e.g. Bcl-xL and Mcl-1) can sequester activated Bak and so prevent Bak homo-oligomerization and pore formation. The role of Bak at the ER membrane is unclear.

Human Bak shares 99.5% amino acid identity with Pan troglodytes, 91.9% identity with Canis lupus familiaris, 86.2% with Bos taurus, 77.2% with Rattus norvegicus. BAK1 is not found in the Danio rerio genome. Human Bak has 53% amino-acid sequence identity with the BH1 and BH2 domains of Bcl-2. Over the full sequence, Bak is 25, 33 and 19% identical to Bcl-2, Bcl-xL and Bax, respectively.

Several Bak single point mutations have been associated with autoimmune diseases, aortic aneurysms, and cervical, colorectal and gastric cancers, although the causal relationship is not clear. In addition, around 200 SNPs, with unknown clinical association have been reported in Entrez SNP database.

Somatic mutations were increased in uterine cervical carcinoma (6 from 42) compared with non-neoplastic tissue (0 from 32). While an early study reported somatic mutations in 17% of samples of colorectal and gastric cancers in Korean patients, a later study reported no somatic mutations in 192 colorectal and gastric cancers.