tion also occurred in mock-infected cells ( Figure 1C , lane 2). Western blot analysis of cell extracts at 16 h.p.i. clearly showed that ActD treatment strongly inhibited N protein accumulation in rMP12-rLuc-infected cells and rMP12-C13type-infected cells, but not in MP-12-infected cells ( Figure 1C , bottom panels). In summary, ActD treatment had little effect on MP-12 replication, whereas it strongly inhibited the expression of both host and viral proteins in the cells infected with MP-12 lacking the NSs gene, which resulted in poor virus production.