Mutation of the m41 ORF inhibits viral replication.

(A) Fibroblasts were infected with WT MCMV, the Δm41/m41.1 mutant or a revertant (Rev) virus at an MOI = 3. Total cell lysates were prepared at 24 hr pi and immunoblotted with anti-m41, anti-m41.1, or anti-IE1 antibodies. (B) Fibroblasts were infected with the indicated viruses (MOI = 3) and 18 hr later treated with 100 µM etoposide (open columns) or vehicle (filled columns). Cell viability was quantified by Trypan Blue exclusion 24 hr later (n = 4) (C) IC-21 macrophages were infected with the indicated viruses (MOI = 3) and cell viability determined 48 hr pi (n = 4) (D) BALB/c mice were infected with WT MCMV (filled square), Rev virus (filled circle), or Δm41/m41.1 (open diamond), organs were removed at the indicated times pi and viral load per organ determined by plaque assay. Viral titers were quantified in three separate experiments and the data pooled, mean ± S.D. of 6–9 mice per group is plotted. * P<0.05, ** P<0.005, *** P<0.0001. Dotted line indicates the limit of detection of the assay.