Mutants of adenovirus type 5 (Ad5) that lack early region 4 (E4) are defective in the expression of viral late genes. E4 mutants exhibit dramatically reduced levels of both cytoplasmic and nuclear viral late RNAs compared to wild-type virus, due principally to reduced stability of unprocessed viral late RNA in the nucleus of mutant-infected cells. To determine whether E4 products also affect the metabolism of host RNAs in infected cells, steady-state levels of β-actin RNA and triose phosphate isomerase (TPI) RNA were measured in the cytoplasms and nuclei of HeLa cells infected by either wild-type Ad5 or the E4 deletion mutant H5dl1004, and were compared to levels in uninfected HeLa cells. S1 nuclease analyses revealed only slight reductions in β-actin mRNA levels in the cytoplasm and in levels of spliced and unspliced β-actin RNA in the nucleus of cells infected by either Ad5 or H5dl1004. RNase protection analyses showed that cytoplasmic TPI RNA levels were not affected by infection of HeLa cells with either Ad5 or H5dl1004. Steady-state levels of nuclear TPI RNA, both spliced and unspliced, were slightly reduced in cells infected by wild-type virus but not in HeLa cells infected by H5dl1004. These results indicate that the reduced stability of RNA in HeLa cells infected by E4 mutants is a virus-specific phenotype which does not extend to host cell RNAs.
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