p73, a recently identified gene highly homologous to p53, can transactivate p53 
target genes and induce apoptosis. Here we report the identification of an 
NH(2)-terminal truncated isoform of human p73, DeltaNp73, which is capable of 
suppressing p53- and p73-dependent transactivation. We speculate that this 
suppression is achieved by competing for the DNA binding site in the case of p53 
and by direct association in the case of TAp73. Expression of DeltaNp73 in 
cancer cell lines also inhibited suppressive activity of p53 and TAp73 in colony 
formation, implying possible involvement of DeltaNp73 in oncogenesis by 
inhibiting the tumor-suppressive function of p53 and TAp73. Also reported is the 
identification of TAp73eta, a new member of the COOH-terminal truncated isoform 
of p73 and tissue-specific expression of these isoforms, along with other 
previously identified p73 isoforms.