To determine cellular DNA content, cells were trypsinized, collected by low-speed centrifugation, fixed, and permeabilized in ice-cold 70% ethanol overnight. Cells were stained with propidium iodide only, or double-stained with propidium iodide and anti-pUL44 antibody to identify HCMV-infected cells. Total or pUL44positive cells were determined for their DNA content by cell-cycle analysis with flow-cytometry. Percentages of cells in each cell cycle compartment were calculated using CellQuest or FlowJo software. Figure S1 APC8 knockdown by shRNA. MRC-5 cells were transduced with lentivirus expressing shRNA targeting either Luc (negative control) or APC8. Forty-eight hours post transduction, cells were infected with mock, wild-type (ADgfp), or UL21adeletion virus (ADsubUL21a). Cell lysates were collected at 72 hpi and analyzed by immunoblotting. Note that the asterisk-marked bottom band that reacted with the APC8 antibody was nonspecific as it was not affected by the APC8-targting shRNA. (TIF) Figure S2 Amino acid residues PR 109-110 of pUL21a are required for its APC binding during HCMV infection. Cells were infected with indicated virus and MG132 was added to the final concentration of 10 mM at 6 hpi. Cells were collected at 20 hpi and lysates were immunoprecipitated with APC3 antibody. Cell lysates and eluted proteins were analyzed by immunoblotting. (TIF) Figure S3 pUL21a dissociates the APC by promoting degradation of the bridge subcomplex. MRC-5 cells were infected with ADgfp or ADsubUL21a, and MG132 was added to the final concentration of 10 mM at 6 hpi. Cells were collected at 20 hpi and lysates were immunoprecipitated with APC3 antibody. Both cell lysates and eluted proteins were analyzed by immunoblotting. (TIF) Figure S4 APC8 is not required for pUL21a-mediated degradation of APC4 and APC5. Knockdown and subsequent immunoblot were performed as described in the legend to Figure  S1 .  Deciphering Novel Host–Herpesvirus Interactions by Virion Proteomics Over the years, a vast array of information concerning the interactions of viruses with their hosts has been collected. However, recent advances in proteomics and other system biology techniques suggest these interactions are far more complex than anticipated. One particularly interesting and novel aspect is the analysis of cellular proteins incorporated into mature virions. Though sometimes considered purification contaminants in the past, their repeated detection by different laboratories suggests that a number of these proteins are bona fide viral components, some of which likely contribute to the viral life cycles. The present mini review focuses on cellular proteins detected in herpesviruses. It highlights the common cellular functions of these proteins, their potential implications for host–pathogen interactions, discusses technical limitations, the need for complementing methods and probes potential future research avenues. Over the last decades, many host-pathogen interactions have been characterized using genetics, biochemical, and microscopy approaches. These discoveries relied on mutants, pharmacological reagents, immunoprecipitations, immunofluorescence, electron microscopy, cell fractionation, and Western blotting to name a few of the methods employed. These approaches provided much precious information but, given the typical focus of these approaches on individual molecules, likely only revealed a small portion of the proteins involved. Other methods such as high throughput two-hybrid and genetic screens, nucleic acid arrays, RNA interference, and proteomics are now proving essential tools to tackle the complexity of these interactions. The main advantages of mass spectrometry, for instance, are that it is a fast, sensitive and potentially a quantitative approach to identify putative novel players, particularly when coupled to efficient purification schemes. Already, proteomics revealed how viruses modulate the expression of host proteins (Rassmann et al., 2006; Sun et al., 2008; Tong et al., 2008; Antrobus et al., 2009; Pastorino et al., 2009; Thanthrige-Don et al., 2009; Zandi et al., 2009; Zhang et al., 2009 Zhang et al., , 2010 Coombs et al., 2010; Emmott et al., 2010; Lu et al., 2010 Lu et al., , 2012 Munday et al., 2010; Bartel et al., 2011; Lietzen et al., 2011; Ramirez-Boo et al., 2011; Chou et al., 2012) . A relatively new and interesting field is the characterization of host-pathogen interactions within mature purified virions. As reviewed on several occasions, several studies reported the presence of individual cellular proteins in viral particles (Bernhard et al., 2005; Maxwell and Frappier, 2007; Viswanathan and Fruh, 2007; Friedel and Haas, 2011; Zheng et al., 2011) . This includes vaccinia virus (Krauss et al., 2002) , influenza virus (Shaw et al., 2008) , HIV (Gurer et al., 2002; Cantin et al., 2005; Ott, 2008) , vesicular stomatitis virus (Moerdyk-Schauwecker et al., 2009) , and several herpesviruses (see below). Though these cellular components have often been considered purification contaminants, the presence of similar proteins in both related and unrelated viruses suggests that some of them may be biologically relevant. The identification of virion-associated host proteins could thus lead to the discovery of novel therapeutic tools against viruses. The present review focuses on their identification and putative roles with respect to the proteomics of herpesviruses.