In-cell RNA transcription assay

The Click-iT RNA Imaging Kit (Invitrogen) was used according to the manufacturer's specifications to assess de novo RNA synthesis in situ. Briefly, GFP/GFP-MeVM expressing COS-7 cells (23 h p.t.) or MeV infected Vero/hSLAM cells (11 h post infection) were treated with 1 mM EU (5-ethynyluridine) for 1 h, fixed with 4% formaldehyde, permeabilised with 0.5% Triton X-100, and stained for de novo synthesized RNA using Alexa 594-azide. Cells were then imaged by CLSM. Control cells were treated with actinomycin D (5 μg/ml) for 1 h prior to EU treatment.