To study intraviral protein-protein interactions of herpesviruses we recombinatorially cloned the individual open reading frames of HSV-1, mCMV and EBV into the yeast-two-hybrid (Y2H) vectors pGBKT7-DEST and pGADT7-DEST and tested all pairwise intraviral protein interactions using an array-based Y2H strategy [27] . To address the issue of false negative interactions, viral proteins containing transmembrane domains were cloned both as full-length and as intracellular and/or extracellular domains. From the mCMV Y2H analysis we observed that 33% of the tested preys, and 40% of the baits, gave positive interactions. Similar results were observed with HSV-1 and EBV with ,1/3 of the clones yielding positive interactions (Table S1). In total, the Y2H  analysis revealed 111 interactions for HSV-1, 406 for mCMV and  218 for EBV (Figures 1B, S1 and S2, Tables S2 and S13) . Combined with our previously published interactomes for VZV (173 interactions) and KSHV (123 interactions), we obtained altogether 1,031 intraviral interactions in five herpesviral species (Tables S2 and S13 ). To evaluate the coverage of our five interactomes we performed an extensive literature search which identified 257 previously published interactions for these herpesviruses (including human cytomegalovirus (hCMV) homologues). Of these 257 interactions we were able to detect 24 (9.3%) in at least one virus ( Figures S3 and S4 and Tables S3 and S14). When comparing our EBV interactome with the recently published EBV network by Calderwood et al., 6 out of 43 (13.9%) interactions could be confirmed [24] . Such low confirmation rates are common to Y2H studies, even for studies within the same species, which in general suffer from low coverage [28, 29, 30] . For instance, in a previous study of human interactions only 2.3-8.4% of known interactions were identified [15] . On the other hand, this implies that ,3% of the interactions found in the present study have been published so far in the literature or identified in previous genomewide screens in the case of EBV. In the case of HSV-1 our study added 102 new interactions to the network of already known interactions (coloured grey in Figure 1B ). As is typical for such interaction networks, no apparent structure can easily be recognized.