Covalent modification of the oncogene product Mdm2 by the ubiquitin-related protein SUMO1 protects it from ubiquitination and enhances its E3 ligase activity towards p53 in vitro. Disappearance of ...

These modifications regulate their structure, function, and stability ... is reflected in the existence of over 600 human E3 ligase genes, representing approximately 3% of the human genome.