The E2 Proteins

The papillomavirus E2 proteins regulate viral transcription and replication and therefore play a central role in the viral life-cycle. In BPV1, the full-length E2 gene product is a transcriptional transactivator that activates transcription from several viral promoters by binding to E2 binding sites located within enhancer elements in the LCR (reviewed in [68,75]). BPV1 also encodes two shorter forms of the E2 protein that antagonize the function of the full-length transactivator. The E2 repressors inhibit transcription by binding to and blocking the E2 binding sites and/or by forming heterodimers with the E2 transactivator. The E2 proteins of the human papillomaviruses can also function as transcriptional transactivators and the E2 proteins of oncogenic human papillomaviruses are able to activate E2responsive promoters more efficiently than those of non-oncogenic viruses [47]. However most, though not all, studies find that the full-length E2 proteins of mucosal type viruses repress the activity of the E6 gene promoter [9,12,29,45,82,100].