(A) Expression levels of MCMV mRNAs (lanes 1–4) and proteins (lanes 5–8). J774 cells were first treated with Salmonella carrying pU6 (-, lanes 1–2 and 5–6), pU6-mPR1 (lanes 3 and 7), and pU6-mPR2 (lanes 4 and 8). The cells were then either mock-infected (lanes 1 and 5) or infected with MCMV (lanes 2–4 and 6–8) and were harvested at 12–72 h post infection. In Northern analysis (lanes 1–4), RNA samples (20 μg) were separated on agarose gels, transferred to nitrocellulose membranes, and hybridized to [32P]-radiolabeled probes that contained the sequence of the MCMV 7.2-kb transcript and mPR mRNA. For Western analyses (lanes 5–8), protein samples (30 μg) were separated in SDS-polyacrylamide gels, and the membranes were stained with the antibodies against mouse actin and MCMV mPR. (B) Growth of MCMV in J774 cells that were treated with Salmonella carrying constructs pU6 (SL201), pU6-mPR1 (mPR1), pU6-mPR2 (mPR2), and pU6-TK112 (TK112). Error bars indicate the SD. Error bars that are not evident indicate that the SD was less than or equal to the height of the symbols.