The human papillomavirus type 16 (HPV-16) E7 and adenovirus (Ad) EIA oncoproteins share a common pathway of transformation. They disrupt the cell cycle G~ phase-specific protein complex containing the E2F transcription factor and the regulatory protein Rbl, the retinoblastoma tumour suppressor gene product. In the G1 and S phases of the cell cycle, E7 and E1A bind two other cellular complexes containing the Rbl-related protein p107 and E2F. Ad E1A disrupts both complexes and releases active E2F. In contrast, HPV-16 E7, although it efficiently binds both E2F-pl07 complexes, causes dissociation of the G 1 phase complex only. Using chimeric proteins of HPV-16 E7 and Ad E1A we were able to demonstrate that the ability of E1A to disrupt both G1 and S phase E2F-pl07 complexes is not due to the higher concentration ofAd E1A in the cell, but is an intrinsic property of the Ad E1A transforming region. These data suggest that E1A and E7 may function in cellular transformation in similar, but not identical ways.

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The conserved region 3 (CR3) of the E7 protein of human papillomaviruses contains two CXXC motifs involved in zinc binding and in the homodimerization of the molecule. Studies have suggested that the intact CXXC motifs in the CR3 of HPV16 and HPV18 E7 are required for the in vitro transforming activity of these proteins. CR3 also contains a low anity pRb binding site and is involved in the disruption of the E2F/Rb1 complex. E7 is structurally and functionally related to Adenovirus E1A protein, which also has two CXXC motifs in CR3. However, the Ad E1A transforming activity appears to be independent of the presence of such domains. In fact, this viral protein exists in vivo as two dierent forms of 289 and 243 amino acids. The shorter Ad E1A form (Ad E1A243), where both CXXC motifs are deleted by internal splicing, retains its in vitro transforming activity. We have investigated if the HPV16 E7 CR3 can be functionally replaced by the Ad E1A243 CR3, which lacks both CXXC motifs. A chimeric protein (E7/E1A243) containing the CR1 and CR2 of HPV16 E7 fused to the CR3 of Ad E1A 243 was constructed. The E7/E1A243 while not able to homodimerize in the S. cerevisiae two-hybrid system retains several of the properties of the parental proteins, HPV16 E7 and Ad E1A. It associates with the`pocket' proteins, induces growth in soft agar of NIH3T3 cells and immortalizes rat embryo ®broblasts. These data suggest that the CXXC motifs in CR3 of E7 do not play a direct role in the transforming properties of this viral protein but probably are important for maintaining the correct protein con®guration.

SummaryWe evaluated the in vitro and in vieo antiviral activity of the deoxyribonucleoside analoDlJe 5.iodo·2'·deoxy-cytidine (IDC) combined with the dihydrofolate reduc-. tase inhibitor methotrexate (MTX) on herpes simplex virus types 1 and 2 (HSV-1, HSV-2). The IDC-MTX combination synergistically inhibited HSV-1 and HSV-2 replication in vitro at concentrations that did not reduce cellular viability and was very effective in reducing the severity of cutaneous lesions in the experimental guinea pig model in vivo. The antiviral activity of the IDC-MTX combination in guinea pigs was also compared with that of acyclovir and was demonstrated to be higher.