ACTIVATION OF C-JUN TRANSCRIPTION FACTOR BY SUBSTITUTION OF A CHARGEDRESIDUE IN ITS N-TERMINAL DOMAIN

C-Jun is a cellular transcription factor that can control gene express ion in response to treatment of cells with phorbol esters, growth fact ors, and expression of some oncogenes. The ability of c-Jun to catalyz e the transcription of certain genes is controlled, in part, by change s in the phosphorylation state of specific amino acids in c-Jun. One o f the major sites that is phosphorylated during signal response is Ser 73. Here we show that substitution of a negatively charged aspartic ac id residue at 73 constitutively increased transcriptional activity of c-Jun. The Asp73 substitution also enhanced its availability to bind t o DNA in a whole cell extract without altering its intrinsic DNA bindi ng activity since the intrinsic activity was unaltered for the c-Jun m utant proteins expressed in a bacterial system. The negatively charged Asp substitution may mimic the negative charge of a phosphorylated se rine at 73. The substitution of an uncharged alanine at 73 resulted in Towered activities. The N-terminal end of c-Jun containing these subs titutions was fused to the DNA-binding region of the bovine papilloma virus E2 protein, and was able to confer the same activation propertie s to the fusion protein at the heterologous E2 DNA-binding site. Ser73 lies in a region of c-Jun previously proposed to bind an uncharacteri zed inhibitor, perhaps related to a protein of approximately 17.5 kD t hat coprecipitates along with our c-Jun or the JunE2 fusion products.