Studies on human papillomavirus type 16 have demonstrated that the product of 
the early gene, E7, plays a key role in the immortalization and malignant 
transformation of the host cell. Several of the biological activities of HPV16 
E7 are mediated by inactivation of the members of the pocket protein family, 
pRb, p107 and p130. In this study, we have characterized the in vitro properties 
of five E7 proteins from benign and malignant HPV types (10, 32, 48, 54, 77). We 
show that these E7 proteins associate with pRb and p107 with different 
efficiencies. All E7s increased the proliferative rate of immortalized rodent 
fibroblasts cultured in 10% calf serum containing medium. This property is 
completely independent of their ability to associate with the pocket proteins. 
Furthermore, all E7s, except HPV10 E7, stimulate G1/S progression and activated 
the cyclin E and cyclin A promoter in the absence of growth factors. This 
activity also does not correlate with the E7-efficiency of binding the pocket 
proteins. Together these data provide evidence that different E7s alter the 
regulation of the cell cycle by diverse mechanism(s). Finally, this comparative 
analysis of the different E7 proteins demonstrates that the oncogenicity of a 
HPV type is not determined by the ability of E7 to associate with the pocket 
proteins.