a | RK-13 cells were infected with equine arterivirus (EAV) for 8 h and cryosections were labelled with anti-nsp2 followed by protein-A–gold detection. Scale bar, 0.1 μm. b–d | Cryoimmunoelecron microscopy of RK-13 cells in which EAV proteins nsp2 and nsp3 were expressed in precursor forms using a Sindbis virus vector. Gold labelling detects nsp2 (a,c) and nsp3 (d); arrows indicate selected gold particles. Cells were harvested 8–12 h after infection. Scale bars, 0.1 μm. ER, endoplasmic reticulum. a Reproduced with permission from Ref. 94 © (1999) ASM. b–d Reproduced with permission from Ref. 100 © (2001) Society for General Microbiology.