ubiquitin-protein ligase. Human ubiquitin-protein ligase E3A interacts with the E6 protein of the cancer-associated Human papillomavirus type 16 and Human papillomavirus type 18. The E6/E6-AP complex binds to and targets the P53 tumour-suppressor protein for ubiquitin-mediated proteolysis . [ edit ] References ^ Huibregtse JM, Scheffner M, Beaudenon S, Howley PM