The BH3-only members act as sentinels that selectively trigger apoptosis in response to developmental cues or stress-signals like DNA damages. Widely expressed mammalian BH3-only proteins are thought to act by binding to and neutralizing their pro-survival counterparts. Activation of BH3-only proteins directly or indirectly results in the activation of proapoptotic BAX and BAK to trigger cell death. Anti-apoptotic BCL-2 or BCL-XL may bind and sequester BH3-only molecules to prevent BAX, BAK activation. The individual BH3-only members are held in check by various mechanisms with in the cells. They are recruited for death duties in response to death cues by diverse activation processes.The mechanisms involved in activation and release of BH3-only proteins for apoptosis will be discussed in this section.

The following figure has been reproduced here with the kind permission from the authors.