Papillomavirus E2 trans-activation repressors

A method for isolating mutations yielding E2 homologous polypeptides that repress trans-activation by native E2 proteins comprising the steps of:

• a) producing a population of mutant DNA fragments by mutagenizing a DNA fragment encoding the amino acids of the native minimal DNA binding domain of a papillomavirus E2 protein;
• b) operatively linking said population of DNA fragments to expression control sequences;
• c) inserting said population of DNA fragments operatively linked to expression control sequences into a vector;
• d) transforming a unicellular host with said vector, said host comprising a full-length native E2 gene operatively linked to expression control sequences and a reporter gene whose transcription is activated by dimers comprising full-length native E2 proteins;
• e) screening for clones of transformed hosts that do not display E2 trans-activation;
• f) testing E2 homologous polypeptides from said clones for their ability to dimerize with themselves;
• g) testing said E2 homologous polypeptides for their ability to bind to E2 DNA binding sites;
• h) testing said E2 homologous polypeptides for their ability to repress transcriptional activation by full-length native E2 protein in a eukaryotic cell.