We employed expression plasmids encoding the VSV glycoprotein (VSV-G) (41 (link)), Machupo virus glycoprotein (MACV-GPC) (42 (link)) (kindly provided by M. Farzan), influenza A virus strain A/WSN/33 (H1N1) hemagglutinin and neuraminidase (WSN-HA/NA) (43 (link)), and WT MERS-S (10 (link)), which have been described elsewhere. In addition, we employed overlap extension PCR to generate MERS-S mutants harboring single (L411F, F473S, D510G, and I529T) mutations in the RBD (primer sequences and detailed information on the cloning procedure are available upon request). For all S proteins, we also generated versions containing a C-terminal V5 epitope for detection by immunoblotting. Expression plasmids for TMPRSS2 N-terminally fused to a cMYC epitope and DPP4 N-terminally fused to DsRed (EU827527.1 and DsRed-DPP4) were constructed by amplifying the genetic information from existing expression plasmids and cloning the respective open reading frame (ORF) into the pQCXIP plasmid (kindly provided by A. L. Brass). For the TMPRSS2 expression vector, we further exchanged the selection marker for puromycin resistance by that for blasticidin resistance, which was taken from plasmid pcDNA6/TR vector (8 (link), 44 (link)). All PCR-amplified sequences were subjected to automated sequence analysis (Microsynth SeqLab) to verify their integrity.