Construction of viral protein expression plasmids. Total RNA from GV-infected BHK21 cells was extracted by using RNeasy Mini Kit (Quiagen) which served as a template for cDNA synthesis using random priming oligos and SuperscriptII Reverse Transcriptase (Invitrogen). The viral genome was amplified by PCR using NSDV/GV genome-specific oligos and subsequently blunt-end cloned into pT7Blue (Novagen). All PCRs were performed using proofreading polymerase (KOD; Novagen). The genome of both strains was completely sequenced. Plasmids pcDNA-GV-N and pcDNA-GV-M were made by cloning the complete ORFs of GV S and GV M segments into pcDNA6/V5-His (Invitrogen), expressing C-terminal V5-tagged N and the glyoproteins (only Gc has a V5 tag at its C-terminus). GV L1-169 and L1-1757 were cloned in pcDNA6 with a C-terminal V5 tag. GV L1-667 and L1749-3391 were cloned into pTriEX (Novagen) such that the expressed proteins have a 6xHis tag at the C-terminus. To generate catalytically inactive variants of L1-169 in pcDNA6/V5-His, single amino acid mutations were introduced by overlap PCR mutagenesis. All mutations were confirmed by sequencing the entire open reading frame.