Figure 2.

Pro-survival (anti-apoptotic) mediators such as Mcl-1 have a short half-life and are actively transcribed in some cancer cells by RNA polymerase II, which requires phosphorylation at serine 2 and serine 5 within the heptapeptide repeats that comprise its C-terminal domain (CTD). Cyclin-dependent kinases 7 and 9 phosphorylate these serines, but can be inhibited by cyclin-dependent kinase inhibitors, ultimately leading to decreased levels of anti-apoptotic proteins and therefore increased cell death.