摘要
Mouse double minute （Mdm） genes span an evolutionary timeframe from the ancient eukaryotic placozoa Trichoplox adhaerens to Homo sapiens, implying a significant and possibly conserved cellular role throughout history. Maintenance of DNA integrity and response to DNA damage involve many key regulatory pathways, including precise control over the tumour suppressor pro- tein p53. In most vertebrates, degradation of p53 through proteasomal targeting is primarily mediated by heterodimers of Mdm2 and the Mdm2-related protein Mdm4 （also known as MdmX）. Both Mdm2 and Mdm4 have p53-binding regions, acidic domains, zinc fingers, and C-terminal RING domains that are conserved throughout evolution. Vertebrates typically have both Mdm2 and Mdm# genes, while analyses of sequenced genomes of invertebrate species have identified single Mdm genes, suggesting that a duplication event occurred prior to emergence of jawless vertebrates about 550-440 million years ago. The functional relationship between Mdm and p53 in T. adhaerens, an organism that has existed for 1 billion years, implies that these two proteins have evolved together to maintain a conserved and regulated function.
