SI Legends Supplementary Figure 1 Original gels from Figure 1 Various E2 proteins were induced with the appropriate concentration of CdSO4 for 4 h and the associated protein complexes were purified by immunopurification with anti-FLAG M2 and anti-HA antibodies as described in Materials and Methods. The bound proteins were eluted with 2% sarcosyl from anti-HA agarose following IP with anti-FLAG M2 agarose. (A) The purified E2 complexes were analyzed on a NuPAGE gel and stained with SilverXpress silver staining kit (Invitrogen). (B) The purified E2 complexes were concentrated with acetone precipitation, dissolved in 1X LDS sample loading buffer, and analyzed on a NuPAGE gel followed by staining with Colloidal Blue.. A band for each E2 protein is marked with an arrowhead and strong binding partners marked with open boxes. Supplementary Figure 2 Papillomavirus E2 protein complexes separated by electrophoresis for mass spectrometric analysis. E2 protein complexes were purified by tandem affinity purification using anti-FLAG and antiHA antibodies. Purified E2 protein complexes were separated on 4-12% NuPAGE gels and stained with Colloidal Blue. Bands (marked with arrow heads) and regions (marked with vertical lines) were selected for mass spectrometry and are numbered to match with identified components in Supplementary Table 1. Bands identified as mainly immunoglobulin, are marked *. Molecular weight markers (MW) were electrophoresed in parallel and are indicated to the left of each bgel image (in kDa). (A) FLAG-HA tagged BPV1 E2 (a, b, two different experiments) and Mock (from cells expressing non-tagged BPV1 E2) (B) FLAG-HA tagged HPV8 E2 (a, b, two different experiments) (C) FLAG-HA tagged HPV8 E2delHC (a, b, two different experiments) (D) FLAG-HA tagged E2 protein for 11 different papillomaviruses. Supplementary Table 1 List of all cellular proteins detected in complex with E2 proteins Tab 1 gives an overview of all cellular proteins identified in complex with the E2 proteins shown. The other tabs list all cellular proteins detected in complex with individual E2 proteins with their overall Mascot score. The top three identified peptides are shown, with their individual Mascot scores and expect values listed. For each protein, the corresponding band or region excised from the gels shown in Supplementary Figure 2 is listed.