Immunodetection of cellular GAPDH and plasmid-encoded MeV F protein under the control of the CMV promoter demonstrated that productive transcription in the presence of the compound furthermore coincides with uninterrupted translation and, in the case of F, co-translational insertion into the host secretory system (figure 5B). Furthermore, equivalent levels of proteolytically processed F 1 material in JMN3-003 and vehicleexposed cells indicated that intracellular vesicular transport remains intact in the presence of JMN3-003, since cleavage is mediated by the cellular protease furin in a late-Golgi compartment [1] . In contrast to host-encoded or transiently expressed proteins, expression of virus-encoded proteins in the context of paramyxovirus or orthomyxovirus infection was fully blocked by 100 nM JMN3-003 (figures 5C and D). Thus, these observations demonstrate that the compound efficiently suppresses the expression of virus-encoded proteins, but that this is not due to general interference of the inhibitor with cellular mRNA synthesis or translation. This phenotype suggests possible interference of JMN3-003 with early steps of the viral life cycle, such as entry or viral RdRp activity, as the basis for antiviral activity.