MODULATION OF TRANSCRIPTIONAL ACTIVATION OF THE PROLIFERATING CELL NUCLEAR ANTIGEN PROMOTER BY THE ADENOVIRUS-E1A 243-RESIDUE ONCOPROTEIN DEPENDS ON PROXIMAL ACTIVATORS

Previous analyses defined a proliferating cell nuclear antigen (PCNA) E1A-responsive element (PERE) in the PCNA promoter that is essential f or transactivation by the 243-residue product of the adenovirus type 2 E1A 12S mRNA (E1A 243R). In this report, we show that the PERE activa tes a heterologous basal promoter and confers susceptibility to transa ctivation by E1A 243R, indicating that the PERE is both necessary and sufficient for the response of the PCNA promoter to this oncoprotein. Insertion of linker sequences between the PERE and the site of transcr iption initiation in the PCNA promoter severely impairs the promoter's response to E1A 243R transactivation. GAL4 sites can replace the func tion of the PERE in the E1A 243R response of the PCNA basal promoter i f transcriptional activators of suitable strength are supplied as GAL4 fusion proteins. Weak transcriptional activators render the PCNA basa l promoter subject to transactivation by E1A 243R but do not endow the adenovirus E1B basal promoter with a similar response. Strong transcr iptional activators do not support transactivation by E1A 243R, howeve r; instead, E1A reduces the ability of the strong activators to activa te both the PCNA and E1B basal promoters. Although other mechanistic d ifferences might determine the response, the data imply a relationship between the activation strength of promoter-proximal effectors and th e response of the PCNA basal promoter to E1A 243R. These experiments i ndicate that the PERE can function autonomously in mediating transacti vation by E1A 243R and that the PCNA basal promoter is configured in a manner that permits modulation by E1A 243R of transcriptional activat ion by promoter-proximal effectors.