FUNCTIONAL INTERACTIONS WITHIN ADENOVIRUS E1A PROTEIN COMPLEXES

The transforming potential of adenovirus E1A oncogene products derives largely from the formation of complexes with cellular proteins, inclu ding the p105(Rb) tumor suppressor and a related p107 species, p130 an d p300 proteins, and cyclin A (p60(cycA)). Extensive quantitative anal yses using E1A deletion mutants identified unique binding patterns for each of these polypeptides within the amino terminus and conserved re gions 1 and 2 (CR1 and CR2) of E1A proteins. A novel protein, termed p 400, was found by peptide mapping to be related to p300, and, like p30 0, to require the E1A amino terminus and a portion of CR1 for binding. p130 was shown to be related to p107, and like p107, to associate wit h p60(cycA). p107, p130 and p105(Rb) all interacted primarily with CR2 , however, sequences within CR1 and the amino terminus were capable of weak interactions and appeared to function cooperatively with CR2 to bind these proteins. Protein kinase activity present in E1A complexes probably derives at least in part from p60(cycA)-linked p33(cdk2) asso ciated with p107 and p130. In vitro phosphorylation of complexes purif ied by immunoprecipitation resulted in labeling of several proteins. p 60(cycA) was phosphorylated to about the same extent in cyclin A compl exes prepared from either AD5- or mock-infected KB cells, however, tha t of p130 and p107 was dramatically higher in p60(cycA) complexes from infected cells. p300 was also phosphorylated in complexes prepared us ing E1A-specific antibodies. Thus one role of E1A proteins in signal t ransduction and regulation of the cell cycle may be to control the bio logical activity of p107, p130 and p300 by enhancing their phosphoryla tion through complex formation.