FIG. 4.

Proteasome-dependent effect of NSP1 on IRF7 levels. (A) 293T cells were cotransfected with equal amounts of pCMV-IRF7 and pCI-NSP1ΔC17 or pCI-NSP1. Where necessary, the empty pCI vector was also added to normalize amounts of plasmid DNA contained in transfection mixtures. Lysates prepared from the cells were examined at 48 h posttransfection for IRF7, wt NSP1, and PCNA by Western blot assay. (B) Same as in panel A, except that at 48 h posttransfection the culture media over some monolayers was adjusted to 10 μM MG132, an inhibitor of proteasome function. Lysates were prepared 12 h later and analyzed by Western blot assay. (C) Same as in panel B, except that immunoprecipitates were recovered by using IRF7-antibody linked to agarose beads from cellular lysates prepared at 24 posttransfection. The immunoprecipitates were analyzed for IRF7 and wt NSP1 by Western blot assay.