TP53BP1 and infection: Fig 1D demonstrates that cells infected with dl366* contained foci of phosphorylated 53BP1 in 75% of infected cells and these p53BP1-S1778-stained foci surrounded nuclear viral compartments in the infected cells (Fig 1E), similarly to other DDR proteins described previously [6, 31, 40]. In contrast, infection with dl366*+E4orf4 did not result in accumulation of phospho-53BP1 and foci containing p53BP1-S1778 were observed in only 6% of infected cells. Thus the results presented in Fig 1 support the conclusion that E4orf4 inhibits DNA damage signaling.