Final answer:
MDM2 and MDMX are involved in the degradation of the p53 protein, an essential transcription factor for cell cycle regulation and apoptosis. They function as E3 ubiquitin ligases, marking the p53 for destruction by the proteasome when it remains bound to unphosphorylated MDM2.
Step-by-step explanation:
MDM2 and MDMX are important regulatory proteins that are responsible for degrading the p53 protein. p53 is a crucial transcription factor involved in cellular responses to stress and damage, particularly in the DNA-damage response. When it is unphosphorylated, MDM2 can bind to p53, leading to its degradation by the proteasome complex. This process is critical for regulating the levels of p53 within the cell and thus ensuring that the pathways governing cell cycle, DNA repair, and apoptosis operate correctly.
Proteins such as p53, which are targeted for degradation, are typically marked with ubiquitin by a process involving ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2) and ubiquitin ligases (E3). MDM2 is an E3 ubiquitin ligase, which provides the specificity in targeting p53 for degradation by the proteasome. Therefore, any p53 that remains bound to unphosphorylated MDM2 becomes a target for proteasomal degradation. This mechanism ensures that cells incapable of rectifying stress, chemical damage, or DNA damage are directed towards apoptosis to prevent the propagation of damaged cells.