Studies of adenovirus E1A oncoprotein mutants suggest that the association of 
E1A with the retinoblastoma protein (pRB) is necessary for E1A-mediated 
transformation. Mutational analysis of E1A indicates that two regions of pRB are 
required for E1A to form stable complexes with the retinoblastoma protein. In 
addition to pRB binding, these regions are necessary for E1A association with 
several other cellular proteins, including p130, p107, cyclin A, and p33cdk2. 
Here we show that short synthetic peptides containing the pRB-binding sequences 
of E1A are sufficient for interaction with p107, cyclin A, and p130. The E7 
protein of human papillomavirus type 16 contains an element that binds to pRB 
and appears to be functionally homologous to the E1A sequences. Peptides 
containing this region of the E7 protein were able to interact with p107, cyclin 
A, and p130 in addition to pRB. These findings suggest that the common mechanism 
of transformation used by these viral oncogenes involves their association with 
a set of polypeptides.