VIRAL ONCOPROTEINS DISCRIMINATE BETWEEN P53 AND THE P53 HOMOLOG P73

p73 is a recently identified member of the p53 family. Previously it w as shown that p73 can, when overproduced in p53-defective tumor cells, activate p53-responsive promoters and induce apoptosis. In this repor t we describe the generation of anti-p73 monoclonal antibodies and con firm that two previously described p73 isoforms are produced in mammal ian cells. Furthermore, we show that these two isoforms can bind to ca nonical p53 DNA-binding sites in electrophoretic mobility shift assays . Despite the high degree of similarity between p53 and p73, we found that adenovirus E1B 55K, simian virus 40 T, and human papillomavirus E 6 do not physically interact with p73. The observation that viral onco proteins discriminate between p53 and p73 suggests that the functions of these two proteins may differ under physiological conditions. Furth ermore, they suggest that inactivation of p73 may not be required for transformation.