p33 sup ING1 and p53 as mediators of cell fate. p53 can arrest cell proliferation by activating a set of target genes, among which p21/WAF1 is pivotal.

p53 can also induce cell death through apoptosis. This outcome relies, at least in part, on the transcriptional activation (Trcn) of death-promoting genes such as Bax and Fas/ApoI, and of genes involved in the production of reactive oxygen species (ROS).

To exert its cellular effects p53 must first be biochemically activated, typically entailing an increase in cellular levels of p53. As Garkavtsev et al. now report, many of p53's activities are carried out in cooperation with p33 sup ING1, presumably through a physical interaction between the two proteins. But it is not known which signals modulate the activity of p33 sup ING1, and whether p53-mediated apoptosis also requires p33 sup ING1.