AMINO-ACIDS CRITICAL FOR THE FUNCTIONS OF THE BOVINE PAPILLOMAVIRUS TYPE-1 E2 TRANSACTIVATOR

The N-terminal domain of the bovine papillomavirus type 1 E2 protein i s important for viral DNA replication, for transcriptional transactiva tion, and for interaction with the El protein. To determine which resi dues of this 200-amino-acid domain are important for these activities, single conservative amino acid substitutions have been generated in 1 7 residues that are invariant among all papillomavirus E2 proteins. Th e resulting mutated E2 proteins were tested for the ability to support viral DNA replication, activate transcription, and cooperatively bind to the origin of replication with the El protein, We identified five mutated proteins that were completely defective for transcriptional ac tivation and either were defective or could support viral DNA replicat ion at only low levels. However, several of these proteins could still interact efficiently with the El protein, In addition, we identified several mutated proteins that were unable to efficiently cooperatively bind to the origin with the El protein, Although a number of the muta ted proteins demonstrated wild-type activity in all of the functions t ested, only 3 out of 17 mutated viral genomes were able to induce foci in a C127 focus formation assay when the mutations were generated in the background of the entire bovine papillomavirus type 1 genome, This finding suggests that the E2 protein may have additional activities t hat are important for the viral life cycle.