Mass spectrometric identification of sumoylated lysine residues within UL44 was performed after in-gel-digestion of E. coliexpressed and SUMO-modified UL44 with endoproteinase Trypsin. Extracted peptides were analyzed by LC-MSMS on an Orbitrap Velos (ThermoFisherScientific) exactly under the conditions described in Hsiao et al. [45] . Data analysis was performed by the use of software ''ChopNSpice'' [45] in combination with MASCOT as search engine. See Supplementary Material and Methods in Text S1 for details.