Enhanced cell‐free transcription of the ribosomal protein L32 gene by the polyoma virus enhancer PEA3 DNA‐binding protein

The mouse-ribosomal-protein-L32-gene promoter contains a 12-bp sequence motif within the 5'-upstream region termed the beta element which shows significant similarity with the consensus sequence of the polyoma-virus-enhancer PEA3. A cloned PEA3 DNA-binding protein, expressed in Escherichia coli and purified, activates the expression of the ribosomal-protein-L32 gene in a cell-free system. Moreover, the PEA3 protein participates in the formation of the ribosomal-protein-L32-promoter-preinitiation-transcription complex. The preinitiation complex formed with PEA3 is resistant to competition by oligonucleotides containing the beta element. In addition anti-PEA3 serum interacts with a factor in mouse L1210 nuclear extract that binds to the beta element, causing a supershift in a mobility-shift assay. Our study demonstrates for the first time that the PEA3 protein can transactivate a cellular gene in a cell-free transcription system.