THE BPV-1 E2 DNA-CONTACT HELIX CYSTEINE IS REQUIRED FOR TRANSCRIPTIONAL ACTIVATION BUT NOT REPLICATION IN MAMMALIAN-CELLS

The papillomavirus E2 protein contains an amino-terminal region though t necessary and sufficient to support transcriptional activation and a carboxy-terminal region shown to direct sequence-specific DNA binding and dimerization. A cysteine residue in the center of the E2 DNA reco gnition helix is highly conserved among papillomavirus E2 proteins. Mu tations of this cysteine in bovine papillomavirus type 1 E2 to serine and glycine resulted in proteins which failed to activate E2-dependent promoters in mammalian cells. These E2 mutants were DNA-binding compe tent, dimeric, and nuclear. When fused to the VP16 transactivation dom ain, C-terminal regions of E2 containing the mutations at 340 supporte d transcriptional activation, indicating that the heterologous Irans-a ctivation domain did not require cysteine in the DNA-binding helix as did the full-length E2 transactivating protein. Although cysteine-340 was required for transcriptional activation it was not required for DN A replication in vivo. Together, these results suggest that the E2 DNA -binding domain may directly contribute to functions of transcriptiona l activation previously thought limited to the N-terminal domain. (C) 1996 Academic Press, Inc.