FIG. 4.

Expression of E2F activities in quiescent fibroblasts. (A) Production of E2F binding activity in cells infected with recombinant adenoviruses containing either the E2F1 or E2F2 gene. Quiescent MEF cells were infected with either E2F1- or E2F2-expressing recombinant adenovirus or with GFP-expressing recombinant adenovirus as a control. E2F2 virus was infected at three different multiplicities to obtain the same E2F DNA-binding activity as with E2F1. E2F binding activities were analyzed by E2F DNA-binding assay with the nuclear extracts prepared from the infected cells. (B) Induction of cyclin E RNA accumulation in cells expressing E2F activities. Expression of cyclin E mRNA was analyzed by Northern analysis in E2F1- and E2F2-expressing cells. mRNA was prepared from the same cells analyzed for E2F DNA-binding activities in panel A and subjected to Northern analysis using a cyclin E probe.